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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1705.05482 | Pavel Krtous | Valeri P. Frolov, Pavel Krtous, David Kubiznak | Black holes, hidden symmetries, and complete integrability | The review paper, 217 pages, 7 figures. [v3: chapters 1-3 and
appendices rearranged and extensively modified, references added] | Living Rev Relativ (2017) 20:6 | 10.1007/s41114-017-0009-9 | null | gr-qc hep-th math-ph math.MP nlin.SI | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The study of higher-dimensional black holes is a subject which has recently
attracted a vast interest. Perhaps one of the most surprising discoveries is a
realization that the properties of higher-dimensional black holes with the
spherical horizon topology and described by the Kerr-NUT-(A)dS metrics are very
similar to the properties of the well known four-dimensional Kerr metric. This
remarkable result stems from the existence of a single object called the
principal tensor. In our review we discuss explicit and hidden symmetries of
higher-dimensional black holes. We start with the overview of the Liouville
theory of completely integrable systems and introduce Killing and Killing-Yano
objects representing explicit and hidden symmetries. We demonstrate that the
principal tensor can be used as a `seed object' which generates all these
symmetries. It determines the form of the black hole geometry, as well as
guarantees its remarkable properties, such as special algebraic type of the
spacetime, complete integrability of geodesic motion, and separability of the
Hamilton-Jacobi, Klein-Gordon, and Dirac equations. The review also contains a
discussion of different applications of the developed formalism and its
possible generalizations.
| [
{
"created": "Mon, 15 May 2017 23:38:24 GMT",
"version": "v1"
},
{
"created": "Thu, 25 May 2017 23:21:19 GMT",
"version": "v2"
},
{
"created": "Wed, 22 Nov 2017 23:51:18 GMT",
"version": "v3"
}
] | 2018-05-24 | [
[
"Frolov",
"Valeri P.",
""
],
[
"Krtous",
"Pavel",
""
],
[
"Kubiznak",
"David",
""
]
] | The study of higher-dimensional black holes is a subject which has recently attracted a vast interest. Perhaps one of the most surprising discoveries is a realization that the properties of higher-dimensional black holes with the spherical horizon topology and described by the Kerr-NUT-(A)dS metrics are very similar to the properties of the well known four-dimensional Kerr metric. This remarkable result stems from the existence of a single object called the principal tensor. In our review we discuss explicit and hidden symmetries of higher-dimensional black holes. We start with the overview of the Liouville theory of completely integrable systems and introduce Killing and Killing-Yano objects representing explicit and hidden symmetries. We demonstrate that the principal tensor can be used as a `seed object' which generates all these symmetries. It determines the form of the black hole geometry, as well as guarantees its remarkable properties, such as special algebraic type of the spacetime, complete integrability of geodesic motion, and separability of the Hamilton-Jacobi, Klein-Gordon, and Dirac equations. The review also contains a discussion of different applications of the developed formalism and its possible generalizations. |
2303.03104 | Paulo Luz | Paulo Luz and Jos\'e P. S. Lemos | Relativistic cosmology and intrinsic spin of matter: Results and
theorems in Einstein-Cartan theory | 43 pages | Physical Review D 107, 084004 (2023) | 10.1103/PhysRevD.107.084004 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | We start by presenting the general set of structure equations for the 1+3
threading spacetime decomposition in 4 spacetime dimensions, valid for any
theory of gravitation based on a metric compatible affine connection. We then
apply these equations to the study of cosmological solutions of the
Einstein-Cartan theory in which the matter is modeled by a perfect fluid with
intrinsic spin. It is shown that the metric tensor can be described by a
generic FLRW solution. However, due to the presence of torsion the Weyl tensors
might not vanish. The coupling between the torsion and Weyl tensors leads to
the conclusion that, in this cosmological model, the universe must either be
flat or open, excluding definitely the possibility of a closed universe. In the
open case, we derive a wave equation for the traceless part of the magnetic
part of the Weyl tensor and show how the intrinsic spin of matter in a dynamic
universe leads to the generation and emission of gravitational waves. Lastly,
in this cosmological model, it is found that the torsion tensor, which has an
intrinsic spin as its source, contributes to a positive accelerated expansion
of the universe. Comparing the theoretical predictions of the model with the
current experimental data, we conclude that torsion cannot completely replace
the role of a cosmological constant.
| [
{
"created": "Thu, 2 Mar 2023 19:00:04 GMT",
"version": "v1"
}
] | 2023-04-18 | [
[
"Luz",
"Paulo",
""
],
[
"Lemos",
"José P. S.",
""
]
] | We start by presenting the general set of structure equations for the 1+3 threading spacetime decomposition in 4 spacetime dimensions, valid for any theory of gravitation based on a metric compatible affine connection. We then apply these equations to the study of cosmological solutions of the Einstein-Cartan theory in which the matter is modeled by a perfect fluid with intrinsic spin. It is shown that the metric tensor can be described by a generic FLRW solution. However, due to the presence of torsion the Weyl tensors might not vanish. The coupling between the torsion and Weyl tensors leads to the conclusion that, in this cosmological model, the universe must either be flat or open, excluding definitely the possibility of a closed universe. In the open case, we derive a wave equation for the traceless part of the magnetic part of the Weyl tensor and show how the intrinsic spin of matter in a dynamic universe leads to the generation and emission of gravitational waves. Lastly, in this cosmological model, it is found that the torsion tensor, which has an intrinsic spin as its source, contributes to a positive accelerated expansion of the universe. Comparing the theoretical predictions of the model with the current experimental data, we conclude that torsion cannot completely replace the role of a cosmological constant. |
gr-qc/9801090 | James E. Lidsey | James E. Lidsey and J. Maharana | Dualities and Hidden Supersymmetry in String Quantum Cosmology | 18 pages, plain Latex, no figures | null | null | CERN-TH/98-22 | gr-qc hep-th | null | A supersymmetric approach to string quantum cosmology based on the
non-compact, global duality symmetries of the effective action is developed. An
N=2 supersymmetric action is derived whose bosonic component is the
Neveu-Schwarz/Neveu-Schwarz sector of the $(d+1)$--dimensional effective action
compactified on a $d$--torus. A representation for the supercharges is found
and the form of the zero-and one-fermion quantum states is determined. The
purely bosonic component of the wavefunction is unique and manifestly invariant
under the symmetry of the action. The formalism applies to a wide class of
non-linear sigma-models.
| [
{
"created": "Tue, 27 Jan 1998 13:32:41 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Lidsey",
"James E.",
""
],
[
"Maharana",
"J.",
""
]
] | A supersymmetric approach to string quantum cosmology based on the non-compact, global duality symmetries of the effective action is developed. An N=2 supersymmetric action is derived whose bosonic component is the Neveu-Schwarz/Neveu-Schwarz sector of the $(d+1)$--dimensional effective action compactified on a $d$--torus. A representation for the supercharges is found and the form of the zero-and one-fermion quantum states is determined. The purely bosonic component of the wavefunction is unique and manifestly invariant under the symmetry of the action. The formalism applies to a wide class of non-linear sigma-models. |
1402.3252 | John F. Donoghue | John F. Donoghue and Basem Kamal El-Menoufi | Non-local quantum effects in cosmology 1: Quantum memory, non-local FLRW
equations and singularity avoidance | 18 pages, 13 figures - extra references added and minor wording
changes | Phys. Rev. D 89, 104062 (2014) | 10.1103/PhysRevD.89.104062 | ACFI-T14-004 | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss cosmological effects of the quantum loops of massless particles,
which lead to temporal non-localities in the equations of motion governing the
scale factor a(t). For the effects discussed here, loops cause the evolution of
a(t) to depend on the memory of the curvature in the past with a weight that
scales initially as 1/(t-t'). As one of our primary examples we discuss the
situation with a large number of light particles, such that these effects occur
in a region where gravity may still be treated classically. However, we also
describe the effect of quantum graviton loops and the full set of Standard
Model particles. We show that these effects decrease with time in an expanding
phase, leading to classical behavior at late time. In a contracting phase,
within our approximations the quantum results can lead to a bounce-like
behavior at scales below the Planck mass, avoiding the singularities required
classically by the Hawking-Penrose theorems. For conformally invariant fields,
such as the Standard Model with a conformally coupled Higgs, this result is
purely non-local and parameter independent.
| [
{
"created": "Thu, 13 Feb 2014 19:06:23 GMT",
"version": "v1"
},
{
"created": "Tue, 18 Mar 2014 17:57:55 GMT",
"version": "v2"
}
] | 2014-06-11 | [
[
"Donoghue",
"John F.",
""
],
[
"El-Menoufi",
"Basem Kamal",
""
]
] | We discuss cosmological effects of the quantum loops of massless particles, which lead to temporal non-localities in the equations of motion governing the scale factor a(t). For the effects discussed here, loops cause the evolution of a(t) to depend on the memory of the curvature in the past with a weight that scales initially as 1/(t-t'). As one of our primary examples we discuss the situation with a large number of light particles, such that these effects occur in a region where gravity may still be treated classically. However, we also describe the effect of quantum graviton loops and the full set of Standard Model particles. We show that these effects decrease with time in an expanding phase, leading to classical behavior at late time. In a contracting phase, within our approximations the quantum results can lead to a bounce-like behavior at scales below the Planck mass, avoiding the singularities required classically by the Hawking-Penrose theorems. For conformally invariant fields, such as the Standard Model with a conformally coupled Higgs, this result is purely non-local and parameter independent. |
2104.01191 | Toby Ord | Toby Ord | The Edges of Our Universe | 45 pages, 16 figures | null | null | null | gr-qc hep-th physics.hist-ph | http://creativecommons.org/licenses/by-nc-nd/4.0/ | This paper explores the fundamental causal limits on how much of the universe
we can observe or affect. It distinguishes four principal regions: the
affectable universe, the observable universe, the eventually observable
universe, and the ultimately observable universe. It then shows how these (and
other) causal limits set physical bounds on what spacefaring civilisations
could achieve over the longterm future.
| [
{
"created": "Fri, 2 Apr 2021 18:29:41 GMT",
"version": "v1"
},
{
"created": "Wed, 5 May 2021 14:41:13 GMT",
"version": "v2"
}
] | 2021-05-06 | [
[
"Ord",
"Toby",
""
]
] | This paper explores the fundamental causal limits on how much of the universe we can observe or affect. It distinguishes four principal regions: the affectable universe, the observable universe, the eventually observable universe, and the ultimately observable universe. It then shows how these (and other) causal limits set physical bounds on what spacefaring civilisations could achieve over the longterm future. |
2107.11616 | Junji Jia | Zixiao Li, Haotian Liu and Junji Jia | Deflection and gravitational lensing of null and timelike signals in
general asymptotically (anti-)de Sitter spacetimes | 20 pages, 5 figures | Phys. Rev. D 104, 084027 (2021) | 10.1103/PhysRevD.104.084027 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The deflection and gravitational lensing of light and massive particles in
arbitrary static, spherically symmetric and asymptotically (anti-)de Sitter
spacetimes are considered in this work. We first proved that for spacetimes
whose metric satisfying certain conditions, the deflection of null rays with
fixed closest distance will not depend on the cosmological constant $\Lambda$,
while that of timelike signals and the apparent angle in gravitational lensing
still depend on $\Lambda$. A two-step perturbative method is then developed to
compute the change of the angular coordinate and total travel time in the weak
field limit. The results are quasi-series of two small quantities, with the
finite distance effect of the source/detector naturally taken into account.
These results are verified by applying to some known de Sitter spacetimes.
Using an exact gravitational lensing equation, we solved the apparent angles of
the images and time delays between them and studied the effect of $\Lambda$ on
them. It is found that generally, a small positive $\Lambda$ will decrease the
apparent angle of images from both sides of the lens and increase the time
delay between them. The time delay between signals from the same side of the
lens but with different energy however, will be decreased by $\Lambda$.
| [
{
"created": "Sat, 24 Jul 2021 14:11:09 GMT",
"version": "v1"
}
] | 2021-10-13 | [
[
"Li",
"Zixiao",
""
],
[
"Liu",
"Haotian",
""
],
[
"Jia",
"Junji",
""
]
] | The deflection and gravitational lensing of light and massive particles in arbitrary static, spherically symmetric and asymptotically (anti-)de Sitter spacetimes are considered in this work. We first proved that for spacetimes whose metric satisfying certain conditions, the deflection of null rays with fixed closest distance will not depend on the cosmological constant $\Lambda$, while that of timelike signals and the apparent angle in gravitational lensing still depend on $\Lambda$. A two-step perturbative method is then developed to compute the change of the angular coordinate and total travel time in the weak field limit. The results are quasi-series of two small quantities, with the finite distance effect of the source/detector naturally taken into account. These results are verified by applying to some known de Sitter spacetimes. Using an exact gravitational lensing equation, we solved the apparent angles of the images and time delays between them and studied the effect of $\Lambda$ on them. It is found that generally, a small positive $\Lambda$ will decrease the apparent angle of images from both sides of the lens and increase the time delay between them. The time delay between signals from the same side of the lens but with different energy however, will be decreased by $\Lambda$. |
gr-qc/9912063 | Cenalo Vaz | T. P. Singh (Tata Institute, Mumbai) and Cenalo Vaz (Univ. Algarve,
Portugal) | Quantum Radiation from Black Holes and Naked Singularities in Spherical
Dust Collapse | PHYZZX macros, 27 pages, 3 figures | Phys.Rev. D61 (2000) 124005 | 10.1103/PhysRevD.61.124005 | UATP-99/04 | gr-qc hep-th | null | A sufficiently massive collapsing star will end its life as a spacetime
singularity. The nature of the Hawking radiation emitted during collapse
depends critically on whether the star's boundary conditions are such as would
lead to the eventual formation of a black hole or, alternatively, to the
formation of a naked singularity. This latter possibility is not excluded by
the singularity theorems. We discuss the nature of the Hawking radiation
emitted in each case. We justify the use of Bogoliubov transforms in the
presence of a Cauchy horizon and show that if spacetime is assumed to terminate
at the Cauchy horizon, the resulting spectrum is thermal, but with a
temperature different from the Hawking temperature.
| [
{
"created": "Wed, 15 Dec 1999 13:58:54 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Singh",
"T. P.",
"",
"Tata Institute, Mumbai"
],
[
"Vaz",
"Cenalo",
"",
"Univ. Algarve,\n Portugal"
]
] | A sufficiently massive collapsing star will end its life as a spacetime singularity. The nature of the Hawking radiation emitted during collapse depends critically on whether the star's boundary conditions are such as would lead to the eventual formation of a black hole or, alternatively, to the formation of a naked singularity. This latter possibility is not excluded by the singularity theorems. We discuss the nature of the Hawking radiation emitted in each case. We justify the use of Bogoliubov transforms in the presence of a Cauchy horizon and show that if spacetime is assumed to terminate at the Cauchy horizon, the resulting spectrum is thermal, but with a temperature different from the Hawking temperature. |
1006.3529 | Paul Wesson | Paul S. Wesson | Physical Identifications for the Algebraic Quantities of
Five-Dimensional Relativity | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | When four-dimensional general relativity is embedded in an unconstrained
man-ner in a fifth dimension, the physical quantities of spacetime can be
interpreted as geometrical properties related to the extra dimension. It has
become widespread to view the ten Einstein equations and the source terms of
the energy-momentum tensor in this way. We now assign physical meanings to the
other five equations involved. The scalar field acts like gravity, but concerns
inertial as opposed to gravitational mass. The other four equations are
conservation laws for 4D dynamics, but where the mass of a test particle is
related to a local value of the cosmological 'constant'. Ways of testing these
identifications are suggested.
| [
{
"created": "Thu, 17 Jun 2010 17:28:39 GMT",
"version": "v1"
}
] | 2010-06-18 | [
[
"Wesson",
"Paul S.",
""
]
] | When four-dimensional general relativity is embedded in an unconstrained man-ner in a fifth dimension, the physical quantities of spacetime can be interpreted as geometrical properties related to the extra dimension. It has become widespread to view the ten Einstein equations and the source terms of the energy-momentum tensor in this way. We now assign physical meanings to the other five equations involved. The scalar field acts like gravity, but concerns inertial as opposed to gravitational mass. The other four equations are conservation laws for 4D dynamics, but where the mass of a test particle is related to a local value of the cosmological 'constant'. Ways of testing these identifications are suggested. |
gr-qc/0409049 | Irina Dymnikova | Irina Dymnikova and Evgeny Galaktionov | Stability of a vacuum nonsingular black hole | 18 pages, 8 figures, submitted to "Classical and Quantum Gravity" | Class.Quant.Grav. 22 (2005) 2331-2358 | 10.1088/0264-9381/22/12/003 | null | gr-qc | null | This is the first of series of papers in which we investigate stability of
the spherically symmetric space-time with de Sitter center. Geometry,
asymptotically Schwarzschild for large $r$ and asymptotically de Sitter as
$r\to 0$, describes a vacuum nonsingular black hole for $m\geq m_{cr}$ and
particle-like self-gravitating structure for $m < m_{cr}$ where a critical
value $m_{cr}$ depends on the scale of the symmetry restoration to de Sitter
group in the origin. In this paper we address the question of stability of a
vacuum non-singular black hole with de Sitter center to external perturbations.
We specify first two types of geometries with and without changes of topology.
Then we derive the general equations for an arbitrary density profile and show
that in the whole range of the mass parameter $m$ objects described by
geometries with de Sitter center remain stable under axial perturbations. In
the case of the polar perturbations we find criteria of stability and study in
detail the case of the density profile $\rho(r)=\rho_0 e^{-r^3/r_0^2 r_g}$
where $\rho_0$ is the density of de Sitter vacuum at the center, $r_0$ is de
Sitter radius and $r_g$ is the Schwarzschild radius.
| [
{
"created": "Sun, 12 Sep 2004 14:49:10 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Dymnikova",
"Irina",
""
],
[
"Galaktionov",
"Evgeny",
""
]
] | This is the first of series of papers in which we investigate stability of the spherically symmetric space-time with de Sitter center. Geometry, asymptotically Schwarzschild for large $r$ and asymptotically de Sitter as $r\to 0$, describes a vacuum nonsingular black hole for $m\geq m_{cr}$ and particle-like self-gravitating structure for $m < m_{cr}$ where a critical value $m_{cr}$ depends on the scale of the symmetry restoration to de Sitter group in the origin. In this paper we address the question of stability of a vacuum non-singular black hole with de Sitter center to external perturbations. We specify first two types of geometries with and without changes of topology. Then we derive the general equations for an arbitrary density profile and show that in the whole range of the mass parameter $m$ objects described by geometries with de Sitter center remain stable under axial perturbations. In the case of the polar perturbations we find criteria of stability and study in detail the case of the density profile $\rho(r)=\rho_0 e^{-r^3/r_0^2 r_g}$ where $\rho_0$ is the density of de Sitter vacuum at the center, $r_0$ is de Sitter radius and $r_g$ is the Schwarzschild radius. |
2307.13249 | Cosimo Bambi | Cosimo Bambi | Regular Black Holes: Towards a New Paradigm of Gravitational Collapse | 4 pages, no figures. Preface and table of contents of the book
"Regular Black Holes: Towards a New Paradigm of Gravitational Collapse"
(Springer Singapore, 2023). ISBN: 978-981-99-1595-8 (Hardcover),
978-981-99-1596-5 (eBook) | null | 10.1007/978-981-99-1596-5 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black holes are one of the most fascinating predictions of general
relativity. They are the natural product of the complete gravitational collapse
of matter and today we have a body of observational evidence supporting the
existence of black holes in the Universe. However, general relativity predicts
that at the center of black holes there are spacetime singularities, where
predictability is lost and standard physics breaks down. It is widely believed
that spacetime singularities are a symptom of the limitations of general
relativity and must be solved within a theory of quantum gravity. Since we do
not have yet any mature and reliable candidate for a quantum gravity theory,
researchers have studied toy-models of singularity-free black holes and of
singularity-free gravitational collapses in order to explore possible
implications of the yet unknown theory of quantum gravity. This book reviews
all main models of regular black holes and non-singular gravitational collapses
proposed in the literature, and discuss the theoretical and observational
implications of these scenarios.
| [
{
"created": "Tue, 25 Jul 2023 04:38:22 GMT",
"version": "v1"
}
] | 2023-07-26 | [
[
"Bambi",
"Cosimo",
""
]
] | Black holes are one of the most fascinating predictions of general relativity. They are the natural product of the complete gravitational collapse of matter and today we have a body of observational evidence supporting the existence of black holes in the Universe. However, general relativity predicts that at the center of black holes there are spacetime singularities, where predictability is lost and standard physics breaks down. It is widely believed that spacetime singularities are a symptom of the limitations of general relativity and must be solved within a theory of quantum gravity. Since we do not have yet any mature and reliable candidate for a quantum gravity theory, researchers have studied toy-models of singularity-free black holes and of singularity-free gravitational collapses in order to explore possible implications of the yet unknown theory of quantum gravity. This book reviews all main models of regular black holes and non-singular gravitational collapses proposed in the literature, and discuss the theoretical and observational implications of these scenarios. |
2206.09518 | Xin Wu | Wenfu Cao, Wenfang Liu and Xin Wu | Integrability of Kerr-Newman spacetime with cloud strings, quintessence
and electromagnetic field | 14 pages, 5 figures and 2 tables | Physical Review D 105, 124039 (2022) | 10.1103/PhysRevD.105.124039 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The dynamics of charged particles moving around a Kerr-Newman black hole
surrounded by cloud strings, quintessence and electromagnetic field is
integrable due to the presence of a fourth constant of motion like the Carter
constant. The fourth motion constant and the axial-symmetry of the spacetime
give a chance to the existence of radial effective potentials with stable
circular orbits in two-dimensional planes, such as the equatorial plane and
other nonequatorial planes. They also give a possibility of the presence of
radial effective potentials with stable spherical orbits in the
three-dimensional space. The dynamical parameters play important roles in
changing the graphs of the effective potentials. In addition, variations of
these parameters affect the presence or absence of stable circular orbits,
innermost stable circular orbits, stable spherical orbits and marginally stable
spherical orbits. They also affect the radii of the stable circular or
spherical orbits. It is numerically shown that the stable circular orbits and
innermost stable circular orbits can exist not only in the equatorial plane but
also in the nonequatorial planes. Several stable spherical orbits and
marginally stable spherical orbits are numerically confirmed, too. In
particular, there are some stable spherical orbits and marginally stable
spherical orbits with vanishing angular momenta for covering whole the range of
the latitudinal coordinate.
| [
{
"created": "Mon, 20 Jun 2022 00:38:49 GMT",
"version": "v1"
}
] | 2022-06-22 | [
[
"Cao",
"Wenfu",
""
],
[
"Liu",
"Wenfang",
""
],
[
"Wu",
"Xin",
""
]
] | The dynamics of charged particles moving around a Kerr-Newman black hole surrounded by cloud strings, quintessence and electromagnetic field is integrable due to the presence of a fourth constant of motion like the Carter constant. The fourth motion constant and the axial-symmetry of the spacetime give a chance to the existence of radial effective potentials with stable circular orbits in two-dimensional planes, such as the equatorial plane and other nonequatorial planes. They also give a possibility of the presence of radial effective potentials with stable spherical orbits in the three-dimensional space. The dynamical parameters play important roles in changing the graphs of the effective potentials. In addition, variations of these parameters affect the presence or absence of stable circular orbits, innermost stable circular orbits, stable spherical orbits and marginally stable spherical orbits. They also affect the radii of the stable circular or spherical orbits. It is numerically shown that the stable circular orbits and innermost stable circular orbits can exist not only in the equatorial plane but also in the nonequatorial planes. Several stable spherical orbits and marginally stable spherical orbits are numerically confirmed, too. In particular, there are some stable spherical orbits and marginally stable spherical orbits with vanishing angular momenta for covering whole the range of the latitudinal coordinate. |
2004.02261 | Dao-Jun Liu | Xing-Hua Jin, Yuan-Xing Gao and Dao-Jun Liu | Strong gravitational lensing of a 4-dimensional Einstein-Gauss-Bonnet
black hole in homogeneous plasma | 16 pages, 7 figures; v2: references added, words polished and some
typos corrected; v3: version to appear in IJMPD | null | 10.1142/S0218271820500650 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the strong gravitational lensing of spherically symmetric
black holes in the novel Einstein-Gauss-Bonnet(EGB) gravity surrounded by
unmagnetised plasma medium. The deflection angle in the strong deflection limit
in EGB spacetime with homogeneous plasma is derived. We find that both the
coupling constant $\alpha$ in the novel EGB gravity and the presence of plasma
can affect the radius of photon sphere, strong field limit coefficient and
other lensing observables significantly. While plasma has little effect on the
angular image separation and the relative magnifications as $\alpha/M^2\to -8$
and $\alpha/M^2\to 1$, respectively.
| [
{
"created": "Sun, 5 Apr 2020 17:31:34 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Apr 2020 05:27:52 GMT",
"version": "v2"
},
{
"created": "Tue, 30 Jun 2020 06:53:44 GMT",
"version": "v3"
}
] | 2020-08-26 | [
[
"Jin",
"Xing-Hua",
""
],
[
"Gao",
"Yuan-Xing",
""
],
[
"Liu",
"Dao-Jun",
""
]
] | We investigate the strong gravitational lensing of spherically symmetric black holes in the novel Einstein-Gauss-Bonnet(EGB) gravity surrounded by unmagnetised plasma medium. The deflection angle in the strong deflection limit in EGB spacetime with homogeneous plasma is derived. We find that both the coupling constant $\alpha$ in the novel EGB gravity and the presence of plasma can affect the radius of photon sphere, strong field limit coefficient and other lensing observables significantly. While plasma has little effect on the angular image separation and the relative magnifications as $\alpha/M^2\to -8$ and $\alpha/M^2\to 1$, respectively. |
gr-qc/9506063 | Gilles Esposito-Farese | Thibault Damour and Gilles Esposito-Farese | Testing gravity to second post-Newtonian order: a field-theory approach | 63 pages, 11 figures.ps.tar.gz.uu, REVTeX 3.0 | Phys.Rev.D53:5541-5578,1996 | 10.1103/PhysRevD.53.5541 | IHES/P/95/57 and CPT-95/P.3167 | gr-qc | null | A new, field-theory-based framework for discussing and interpreting tests of
gravity, notably at the second post-Newtonian (2PN) level, is introduced.
Contrary to previous frameworks which attempted at parametrizing any
conceivable deviation from general relativity, we focus on the best motivated
class of models, in which gravity is mediated by a tensor field together with
one or several scalar fields. The 2PN approximation of these
"tensor-multi-scalar" theories is obtained thanks to a diagrammatic expansion
which allows us to compute the Lagrangian describing the motion of N bodies. In
contrast with previous studies which had to introduce many phenomenological
parameters, we find that the 2PN deviations from general relativity can be
fully described by only two new 2PN parameters, epsilon and zeta, beyond the
usual (Eddington) 1PN parameters beta and gamma. It follows from the basic
tenets of field theory, notably the absence of negative-energy excitations,
that (beta-1), epsilon and zeta (as well as any new parameter entering higher
post-Newtonian orders) must tend to zero with (gamma-1). It is also found that
epsilon and zeta do not enter the 2PN equations of motion of light. Therefore,
light-deflection or time-delay experiments cannot probe any theoretically
motivated 2PN deviation from general relativity, but they can give a clean
access to (gamma-1), which is of greatest significance as it measures the basic
coupling strength of matter to the scalar fields. Because of the importance of
self-gravity effects in neutron stars, binary-pulsar experiments are found to
constitute a unique testing ground for the 2PN structure of gravity. A
simplified analysis of four binary pulsars already leads to significant
constraints: |epsilon| < 7x10^-2, |zeta| < 6x10^-3.
| [
{
"created": "Tue, 27 Jun 1995 19:05:20 GMT",
"version": "v1"
}
] | 2011-09-09 | [
[
"Damour",
"Thibault",
""
],
[
"Esposito-Farese",
"Gilles",
""
]
] | A new, field-theory-based framework for discussing and interpreting tests of gravity, notably at the second post-Newtonian (2PN) level, is introduced. Contrary to previous frameworks which attempted at parametrizing any conceivable deviation from general relativity, we focus on the best motivated class of models, in which gravity is mediated by a tensor field together with one or several scalar fields. The 2PN approximation of these "tensor-multi-scalar" theories is obtained thanks to a diagrammatic expansion which allows us to compute the Lagrangian describing the motion of N bodies. In contrast with previous studies which had to introduce many phenomenological parameters, we find that the 2PN deviations from general relativity can be fully described by only two new 2PN parameters, epsilon and zeta, beyond the usual (Eddington) 1PN parameters beta and gamma. It follows from the basic tenets of field theory, notably the absence of negative-energy excitations, that (beta-1), epsilon and zeta (as well as any new parameter entering higher post-Newtonian orders) must tend to zero with (gamma-1). It is also found that epsilon and zeta do not enter the 2PN equations of motion of light. Therefore, light-deflection or time-delay experiments cannot probe any theoretically motivated 2PN deviation from general relativity, but they can give a clean access to (gamma-1), which is of greatest significance as it measures the basic coupling strength of matter to the scalar fields. Because of the importance of self-gravity effects in neutron stars, binary-pulsar experiments are found to constitute a unique testing ground for the 2PN structure of gravity. A simplified analysis of four binary pulsars already leads to significant constraints: |epsilon| < 7x10^-2, |zeta| < 6x10^-3. |
1704.07786 | Sergey Chervon | Igor V. Fomin and Sergey V. Chervon | A new approach to exact solutions construction in scalar cosmology with
a Gauss-Bonnet term | 12 pages, 1 figure | Modern Physics Letters A, Vol.32, No.25 (2017) 1750129 (14 pages) | 10.1142/S0217732317501292 | LGCA2017/CH2; LMME2017/F2 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the cosmological model based on Einstein-Gauss-Bonnet gravity with
non-minimal coupling of a scalar field to a Gauss-Bonnet term in 4D Friedmann
universe. We show how constructing the exact solutions by the method based on a
confrontation of the Hubble parameter in the model under consideration with
that in a standard scalar field inflationary cosmology.
| [
{
"created": "Tue, 25 Apr 2017 17:00:32 GMT",
"version": "v1"
}
] | 2017-07-26 | [
[
"Fomin",
"Igor V.",
""
],
[
"Chervon",
"Sergey V.",
""
]
] | We study the cosmological model based on Einstein-Gauss-Bonnet gravity with non-minimal coupling of a scalar field to a Gauss-Bonnet term in 4D Friedmann universe. We show how constructing the exact solutions by the method based on a confrontation of the Hubble parameter in the model under consideration with that in a standard scalar field inflationary cosmology. |
2107.02449 | Stefan Czimek | Stefanos Aretakis, Stefan Czimek, Igor Rodnianski | The characteristic gluing problem for the Einstein vacuum equations.
Linear and non-linear analysis | 102 pages, 11 figures | null | null | null | gr-qc math-ph math.AP math.DG math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This is the second paper in a series of papers adressing the characteristic
gluing problem for the Einstein vacuum equations. We solve the codimension-$10$
characteristic gluing problem for characteristic data which are close to the
Minkowski data. We derive an infinite-dimensional space of gauge-dependent
charges and a $10$-dimensional space of gauge-invariant charges that are
conserved by the linearized null constraint equations and act as obstructions
to the gluing problem. The gauge-dependent charges can be matched by applying
angular and transversal gauge transformations of the characteristic data. By
making use of a special hierarchy of radial weights of the null constraint
equations, we construct the null lapse function and the conformal geometry of
the characteristic hypersurface, and we show that the aforementioned charges
are in fact the only obstructions to the gluing problem. Modulo the
gauge-invariant charges, the resulting solution of the null constraint
equations is $C^{m+2}$ for any specified integer $m\geq0$ in the tangential
directions and $C^2$ in the transversal directions to the characteristic
hypersurface. We also show that higher-order (in all directions) gluing is
possible along bifurcated characteristic hypersurfaces (modulo the
gauge-invariant charges).
| [
{
"created": "Tue, 6 Jul 2021 07:54:40 GMT",
"version": "v1"
}
] | 2021-07-07 | [
[
"Aretakis",
"Stefanos",
""
],
[
"Czimek",
"Stefan",
""
],
[
"Rodnianski",
"Igor",
""
]
] | This is the second paper in a series of papers adressing the characteristic gluing problem for the Einstein vacuum equations. We solve the codimension-$10$ characteristic gluing problem for characteristic data which are close to the Minkowski data. We derive an infinite-dimensional space of gauge-dependent charges and a $10$-dimensional space of gauge-invariant charges that are conserved by the linearized null constraint equations and act as obstructions to the gluing problem. The gauge-dependent charges can be matched by applying angular and transversal gauge transformations of the characteristic data. By making use of a special hierarchy of radial weights of the null constraint equations, we construct the null lapse function and the conformal geometry of the characteristic hypersurface, and we show that the aforementioned charges are in fact the only obstructions to the gluing problem. Modulo the gauge-invariant charges, the resulting solution of the null constraint equations is $C^{m+2}$ for any specified integer $m\geq0$ in the tangential directions and $C^2$ in the transversal directions to the characteristic hypersurface. We also show that higher-order (in all directions) gluing is possible along bifurcated characteristic hypersurfaces (modulo the gauge-invariant charges). |
2212.02572 | Geraint Pratten | Geraint Pratten, Antoine Klein, Christopher J. Moore, Hannah
Middleton, Nathan Steinle, Patricia Schmidt, Alberto Vecchio | On the LISA science performance in observations of short-lived signals
from massive black hole binary coalescences | 13 pages, 6 figures, comments welcome! | null | 10.1103/PhysRevD.107.123026 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | The observation of massive black hole binary systems is one of the main
science objectives of the Laser Interferometer Space Antenna (LISA). The
instrument's design requirements have recently been revised: they set a
requirement at $0.1\,\mathrm{mHz}$, with no additional explicit requirements at
lower frequencies. This has implications for observations of the short-lived
signals produced by the coalescence of massive and high-redshift binaries. Here
we consider the most pessimistic scenario: the (unlikely) case in which LISA
has no sensitivity below $0.1\,\mathrm{mHz}$. We show that the presence of
higher multipoles (beyond the dominant $\ell = |m| = 2$ mode) in the
gravitational radiation from these systems, which will be detectable with a
total signal-to-noise ratio $\sim 10^3$, allows LISA to retain the capability
to accurately measure the physical parameters, the redshift, and to constrain
the sky location. To illustrate this point, we consider a few select binaries
in a total (redshifted) mass range of $4 \times10^6 - 4 \times 10^7\,M_\odot$
whose ($\ell = |m| = 2$) gravitational-wave signals last between $\approx 12$
hours and $\approx 20$ days in band. We model the emitted gravitational
radiation using the highly accurate (spin-aligned) waveform approximant
IMRPhenomXHM and carry out a fully coherent Bayesian analysis on the LISA
noise-orthogonal time-delay-interferometry channels.
| [
{
"created": "Mon, 5 Dec 2022 19:51:48 GMT",
"version": "v1"
}
] | 2023-07-05 | [
[
"Pratten",
"Geraint",
""
],
[
"Klein",
"Antoine",
""
],
[
"Moore",
"Christopher J.",
""
],
[
"Middleton",
"Hannah",
""
],
[
"Steinle",
"Nathan",
""
],
[
"Schmidt",
"Patricia",
""
],
[
"Vecchio",
"Alberto",
... | The observation of massive black hole binary systems is one of the main science objectives of the Laser Interferometer Space Antenna (LISA). The instrument's design requirements have recently been revised: they set a requirement at $0.1\,\mathrm{mHz}$, with no additional explicit requirements at lower frequencies. This has implications for observations of the short-lived signals produced by the coalescence of massive and high-redshift binaries. Here we consider the most pessimistic scenario: the (unlikely) case in which LISA has no sensitivity below $0.1\,\mathrm{mHz}$. We show that the presence of higher multipoles (beyond the dominant $\ell = |m| = 2$ mode) in the gravitational radiation from these systems, which will be detectable with a total signal-to-noise ratio $\sim 10^3$, allows LISA to retain the capability to accurately measure the physical parameters, the redshift, and to constrain the sky location. To illustrate this point, we consider a few select binaries in a total (redshifted) mass range of $4 \times10^6 - 4 \times 10^7\,M_\odot$ whose ($\ell = |m| = 2$) gravitational-wave signals last between $\approx 12$ hours and $\approx 20$ days in band. We model the emitted gravitational radiation using the highly accurate (spin-aligned) waveform approximant IMRPhenomXHM and carry out a fully coherent Bayesian analysis on the LISA noise-orthogonal time-delay-interferometry channels. |
2008.05696 | Ming Zhang | Ming Zhang and Jie Jiang | Revisiting collisional Penrose processes in term of escape probabilities
for spinning particles | 7 pages, 4 captioned figures, PRD accepted | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by-sa/4.0/ | We first study the escape probability of the spinning particle emitted from
the Kerr black hole and find that the escape probability increases with the
spin of the particle around the extreme Kerr black hole; in contrast, the
escape probability decreases at the position near the horizon but increases at
the position far away from the horizon with the increasing spin of the
particle. We then probe the relation between the escape probabilities and the
energy extraction efficiencies of collisional Penrose processes for the
particles with varying spin. For the extreme Kerr black hole, the efficiency
increases with the escape probability; for the non-extreme Kerr black hole, the
near-horizon-efficiency decreases with the escape probability whilst the
efficiency may increase with the escape probability in the ergosphere. In the
event horizon limit, we also find that the average escape probability of the
spinning particle produced in the collisional Penrose process decreases with
the rotation parameter of the Kerr black hole.
| [
{
"created": "Thu, 13 Aug 2020 05:39:09 GMT",
"version": "v1"
}
] | 2020-08-14 | [
[
"Zhang",
"Ming",
""
],
[
"Jiang",
"Jie",
""
]
] | We first study the escape probability of the spinning particle emitted from the Kerr black hole and find that the escape probability increases with the spin of the particle around the extreme Kerr black hole; in contrast, the escape probability decreases at the position near the horizon but increases at the position far away from the horizon with the increasing spin of the particle. We then probe the relation between the escape probabilities and the energy extraction efficiencies of collisional Penrose processes for the particles with varying spin. For the extreme Kerr black hole, the efficiency increases with the escape probability; for the non-extreme Kerr black hole, the near-horizon-efficiency decreases with the escape probability whilst the efficiency may increase with the escape probability in the ergosphere. In the event horizon limit, we also find that the average escape probability of the spinning particle produced in the collisional Penrose process decreases with the rotation parameter of the Kerr black hole. |
0801.1734 | Brandon DiNunno | Brandon S. DiNunno and Richard A. Matzner | The Volume Inside a Black Hole | 17 pages, 5 figures | Gen.Rel.Grav.42:63-76,2010 | 10.1007/s10714-009-0814-x | null | gr-qc | null | The horizon (the surface) of a black hole is a null surface, defined by those
hypothetical "outgoing" light rays that just hover under the influence of the
strong gravity at the surface. Because the light rays are orthogonal to the
spatial 2-dimensional surface at one instant of time, the surface of the black
hole is the same for all observers (i.e. the same for all coordinate
definitions of "instant of time"). This value is 4*(pi)* (2Gm/c^2)^2 for
nonspinning black holes, with G= Newton's constant, c= speed of light, and m=
mass of the black hole.
The 3-dimensional spatial volume inside a black hole, in contrast, depends
explicitly on the definition of time, and can even be time dependent, or zero.
We give examples of the volume found inside a standard, nonspinning spherical
black hole, for several different standard time-coordinate definitions.
Elucidating these results for the volume provides a new pedagogical resource of
facts already known in principle to the relativity community, but rarely worked
out.
| [
{
"created": "Fri, 11 Jan 2008 08:44:01 GMT",
"version": "v1"
}
] | 2010-01-04 | [
[
"DiNunno",
"Brandon S.",
""
],
[
"Matzner",
"Richard A.",
""
]
] | The horizon (the surface) of a black hole is a null surface, defined by those hypothetical "outgoing" light rays that just hover under the influence of the strong gravity at the surface. Because the light rays are orthogonal to the spatial 2-dimensional surface at one instant of time, the surface of the black hole is the same for all observers (i.e. the same for all coordinate definitions of "instant of time"). This value is 4*(pi)* (2Gm/c^2)^2 for nonspinning black holes, with G= Newton's constant, c= speed of light, and m= mass of the black hole. The 3-dimensional spatial volume inside a black hole, in contrast, depends explicitly on the definition of time, and can even be time dependent, or zero. We give examples of the volume found inside a standard, nonspinning spherical black hole, for several different standard time-coordinate definitions. Elucidating these results for the volume provides a new pedagogical resource of facts already known in principle to the relativity community, but rarely worked out. |
gr-qc/0506036 | S. Mignemi | S. Mignemi | A spacetime realization of kappa-Poincare algebra | 5 pages, plain TeX. Some misprints corrected. A discussion on the
possibility of experimental verifications added | Phys.Rev. D72 (2005) 087703 | 10.1103/PhysRevD.72.087703 | null | gr-qc | null | We study a Hamiltonian realization of the phase space of kappa-Poincare
algebra that yields a definition of velocity consistent with the deformed
Lorentz symmetry. We are also able to determine the laws of transformation of
spacetime coordinates and to define an invariant spacetime metric, and discuss
some possible experimental consequences.
| [
{
"created": "Mon, 6 Jun 2005 16:32:57 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Aug 2005 11:11:58 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Mignemi",
"S.",
""
]
] | We study a Hamiltonian realization of the phase space of kappa-Poincare algebra that yields a definition of velocity consistent with the deformed Lorentz symmetry. We are also able to determine the laws of transformation of spacetime coordinates and to define an invariant spacetime metric, and discuss some possible experimental consequences. |
1912.00677 | Fran\c{c}ois Staelens | Fran\c{c}ois Staelens, J\'er\'emy Rekier, Andr\'e F\"uzfa | Universality of the spherical collapse with respect to the matter type :
the case of a barotropic fluid with linear equation of state | 24 pages, 19 figures | Gen Relativ Gravit 53, 38 (2021) | 10.1007/s10714-021-02804-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the spherical collapse of an over-density of a barotropic fluid with
linear equation of state in a cosmological background. Fully relativistic
simulations are performed by using the Baumgarte-Shibata-Shapiro-Nakamura
formalism jointly with the Valencia formulation of the hydrodynamics. This
permits us to test the universality of the critical collapse with respect to
the matter type by considering the constant equation of state parameter
$\omega$ as a control parameter. We exhibit, for a fixed radial profile of the
energy-density contrast, the existence of a critical value $\omega^*$ for the
equation of state parameter under which the fluctuation collapses to a black
hole and above which it is diluting. It is shown numerically that the mass of
the formed black hole, for subcritical solutions, obeys a scaling law $M\propto
|\omega - \omega^*|^\gamma$ with a critical exponent $\gamma$ independent on
the matter type, revealing the universality. This universal scaling law is
shown to be verified in the empty Minkoswki and de Sitter space-times. For the
full matter Einstein-de Sitter universe, the universality is not observed if
conformally flat sub-horizon initial conditions are used. But when
super-horizon initial conditions computed from the long-wavelength
approximation are used, the universality appears to be true.
| [
{
"created": "Mon, 2 Dec 2019 10:43:11 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Apr 2021 09:46:00 GMT",
"version": "v2"
}
] | 2021-04-15 | [
[
"Staelens",
"François",
""
],
[
"Rekier",
"Jérémy",
""
],
[
"Füzfa",
"André",
""
]
] | We study the spherical collapse of an over-density of a barotropic fluid with linear equation of state in a cosmological background. Fully relativistic simulations are performed by using the Baumgarte-Shibata-Shapiro-Nakamura formalism jointly with the Valencia formulation of the hydrodynamics. This permits us to test the universality of the critical collapse with respect to the matter type by considering the constant equation of state parameter $\omega$ as a control parameter. We exhibit, for a fixed radial profile of the energy-density contrast, the existence of a critical value $\omega^*$ for the equation of state parameter under which the fluctuation collapses to a black hole and above which it is diluting. It is shown numerically that the mass of the formed black hole, for subcritical solutions, obeys a scaling law $M\propto |\omega - \omega^*|^\gamma$ with a critical exponent $\gamma$ independent on the matter type, revealing the universality. This universal scaling law is shown to be verified in the empty Minkoswki and de Sitter space-times. For the full matter Einstein-de Sitter universe, the universality is not observed if conformally flat sub-horizon initial conditions are used. But when super-horizon initial conditions computed from the long-wavelength approximation are used, the universality appears to be true. |
0812.1973 | Giampiero Esposito Dr. | Donato Bini, Giampiero Esposito, Roberto Valentino Montaquila | Solution of Maxwell's equations on a de Sitter background | 11 pages, 5 figures, Latex. The presentation has been improved, and
the title has been changed | Gen.Rel.Grav.42:51-61,2010 | 10.1007/s10714-009-0813-y | DSF-2008-29 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Maxwell equations for the electromagnetic potential, supplemented by the
Lorenz gauge condition, are decoupled and solved exactly in de Sitter
space-time studied in static spherical coordinates. There is no source besides
the background. One component of the vector field is expressed, in its radial
part, through the solution of a fourth-order ordinary differential equation
obeying given initial conditions. The other components of the vector field are
then found by acting with lower-order differential operators on the solution of
the fourth-order equation (while the transverse part is decoupled and solved
exactly from the beginning). The whole four-vector potential is eventually
expressed through hypergeometric functions and spherical harmonics. Its radial
part is plotted for given choices of initial conditions. We have thus
completely succeeded in solving the homogeneous vector wave equation for
Maxwell theory in the Lorenz gauge when a de Sitter spacetime is considered,
which is relevant both for inflationary cosmology and gravitational wave
theory. The decoupling technique and analytic formulae and plots are completely
original. This is an important step towards solving exactly the tensor wave
equation in de Sitter space-time, which has important applications to the
theory of gravitational waves about curved backgrounds.
| [
{
"created": "Wed, 10 Dec 2008 17:23:59 GMT",
"version": "v1"
},
{
"created": "Wed, 8 Apr 2009 14:24:46 GMT",
"version": "v2"
}
] | 2009-12-17 | [
[
"Bini",
"Donato",
""
],
[
"Esposito",
"Giampiero",
""
],
[
"Montaquila",
"Roberto Valentino",
""
]
] | The Maxwell equations for the electromagnetic potential, supplemented by the Lorenz gauge condition, are decoupled and solved exactly in de Sitter space-time studied in static spherical coordinates. There is no source besides the background. One component of the vector field is expressed, in its radial part, through the solution of a fourth-order ordinary differential equation obeying given initial conditions. The other components of the vector field are then found by acting with lower-order differential operators on the solution of the fourth-order equation (while the transverse part is decoupled and solved exactly from the beginning). The whole four-vector potential is eventually expressed through hypergeometric functions and spherical harmonics. Its radial part is plotted for given choices of initial conditions. We have thus completely succeeded in solving the homogeneous vector wave equation for Maxwell theory in the Lorenz gauge when a de Sitter spacetime is considered, which is relevant both for inflationary cosmology and gravitational wave theory. The decoupling technique and analytic formulae and plots are completely original. This is an important step towards solving exactly the tensor wave equation in de Sitter space-time, which has important applications to the theory of gravitational waves about curved backgrounds. |
gr-qc/0703039 | Adamantios Stavridis | M. Vavoulidis, A. Stavridis, K.D. Kokkotas and H. Beyer | Torsional Oscillations of Slowly Rotating Relativistic Stars | 6 pages, 1 figure. Accepted for publication to MNRAS | Mon.Not.Roy.Astron.Soc.377:1553-1556,2007 | 10.1111/j.1365-2966.2007.11706.x | null | gr-qc astro-ph | null | We study the effects of rotation on the torsional modes of oscillating
relativistic stars with a solid crust. Earlier works in Newtonian theory
provided estimates of the rotational corrections for the torsional modes and
suggested that they should become CFS unstable, even for quite low rotation
rates. In this work, we study the effect of rotation in the context of general
relativity using elasticity theory and in the slow-rotation approximation. We
find that the Newtonian picture does not change considerably. The inclusion of
relativistic effects leads only to quantitative corrections. The degeneracy of
modes for different values of $m$ is removed, and modes with $\ell=m$ are
shifted towards zero frequencies and become secularly unstable at stellar
rotational frequencies $\sim$ 20-30 Hz.
| [
{
"created": "Tue, 6 Mar 2007 14:22:04 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Vavoulidis",
"M.",
""
],
[
"Stavridis",
"A.",
""
],
[
"Kokkotas",
"K. D.",
""
],
[
"Beyer",
"H.",
""
]
] | We study the effects of rotation on the torsional modes of oscillating relativistic stars with a solid crust. Earlier works in Newtonian theory provided estimates of the rotational corrections for the torsional modes and suggested that they should become CFS unstable, even for quite low rotation rates. In this work, we study the effect of rotation in the context of general relativity using elasticity theory and in the slow-rotation approximation. We find that the Newtonian picture does not change considerably. The inclusion of relativistic effects leads only to quantitative corrections. The degeneracy of modes for different values of $m$ is removed, and modes with $\ell=m$ are shifted towards zero frequencies and become secularly unstable at stellar rotational frequencies $\sim$ 20-30 Hz. |
1309.7533 | Emilio Rub\'in de Celis | E. Rub\'in de Celis, O. P. Santill\'an and C. Simeone | Probing global aspects of a geometry by the self-force on a charge:
Spherical thin-shell wormholes | 17 pages, 4 figues | null | 10.1103/PhysRevD.88.124012 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The self-interaction for a static point charge in the space-time of a
thin-shell wormhole constructed connecting two identical Schwarzschild
geometries is calculated in a series expansion. The electrostatic self-force is
evaluated numerically. It is found to be attractive towards the throat except
for some values of the throat radius proximate to the value of the
Schwarzschild horizon for which the force is repulsive or attractive depending
on the position of the charge. The result differs from the self-force in the
space-time of the Schwarzschild black hole, where it is always repulsive from
the center. Although these wormhole and black hole geometries are locally
indistinguishable, the different topologies of both backgrounds are manifested
in the electrostatic field of a point charge.
| [
{
"created": "Sun, 29 Sep 2013 04:33:32 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Nov 2013 00:29:53 GMT",
"version": "v2"
}
] | 2015-06-17 | [
[
"de Celis",
"E. Rubín",
""
],
[
"Santillán",
"O. P.",
""
],
[
"Simeone",
"C.",
""
]
] | The self-interaction for a static point charge in the space-time of a thin-shell wormhole constructed connecting two identical Schwarzschild geometries is calculated in a series expansion. The electrostatic self-force is evaluated numerically. It is found to be attractive towards the throat except for some values of the throat radius proximate to the value of the Schwarzschild horizon for which the force is repulsive or attractive depending on the position of the charge. The result differs from the self-force in the space-time of the Schwarzschild black hole, where it is always repulsive from the center. Although these wormhole and black hole geometries are locally indistinguishable, the different topologies of both backgrounds are manifested in the electrostatic field of a point charge. |
gr-qc/0407015 | Oleg Teryaev | A.J. Silenko, O.V. Teryaev | Semiclassical limit for Dirac particles interacting with a gravitational
field | 8 pages, no figures; version to appear in Physical Review D | Phys.Rev. D71 (2005) 064016 | 10.1103/PhysRevD.71.064016 | null | gr-qc astro-ph hep-ph hep-th | null | The behavior of spin-1/2 particle in a weak static gravitational field is
considered. The Dirac Hamiltonian is diagonalized by the Foldy-Wouthuysen
transformation providing also the simple form for the momentum and spin
polarization operators. The operator equations of momentum and spin motion are
derived for a first time. Their semiclassical limit is analyzed. The dipole
spin-gravity coupling in the previously found (another) Hamiltonian does not
lead to any observable effects. The general agreement between the quantum and
classical analysis is established, contrary to several recent claims. The
expression for gravitational Stern-Gerlach force is derived. The helicity
evolution in the gravitational field and corresponding accelerated frame
coincides, being the manifestation of the equivalence principle.
| [
{
"created": "Sun, 4 Jul 2004 16:45:03 GMT",
"version": "v1"
},
{
"created": "Tue, 20 Jul 2004 12:44:20 GMT",
"version": "v2"
},
{
"created": "Sun, 27 Feb 2005 18:02:26 GMT",
"version": "v3"
}
] | 2009-11-10 | [
[
"Silenko",
"A. J.",
""
],
[
"Teryaev",
"O. V.",
""
]
] | The behavior of spin-1/2 particle in a weak static gravitational field is considered. The Dirac Hamiltonian is diagonalized by the Foldy-Wouthuysen transformation providing also the simple form for the momentum and spin polarization operators. The operator equations of momentum and spin motion are derived for a first time. Their semiclassical limit is analyzed. The dipole spin-gravity coupling in the previously found (another) Hamiltonian does not lead to any observable effects. The general agreement between the quantum and classical analysis is established, contrary to several recent claims. The expression for gravitational Stern-Gerlach force is derived. The helicity evolution in the gravitational field and corresponding accelerated frame coincides, being the manifestation of the equivalence principle. |
2401.05253 | Albachiara Cogo | Stefano Borghini, Carla Cederbaum, Albachiara Cogo | Black Hole and Equipotential Photon Surface Uniqueness in 4-dimensional
Asymptotically Flat Electrostatic Electro-Vacuum Spacetimes | 63 pages | null | null | null | gr-qc math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study 4-dimensional asymptotically flat electrostatic electro-vacuum
spacetimes with a connected black hole, photon sphere, or equipotential photon
surface inner boundary. Our analysis, inspired by the potential theory approach
by Agostiniani-Mazzieri, allows to give self-contained proofs of known
uniqueness theorems of the sub-extremal, extremal and super-extremal
Reissner-Nordstr\"om spacetimes. We also obtain new results for connected
photon spheres and for connected photon surfaces in the extremal case. Finally,
we provide, up to a restriction on the range of their radii, the uniqueness
result for connected (both non-degenerate and degenerate) photon surfaces in
the super-extremal case, not yet treated in the literature.
| [
{
"created": "Wed, 10 Jan 2024 16:32:01 GMT",
"version": "v1"
}
] | 2024-01-11 | [
[
"Borghini",
"Stefano",
""
],
[
"Cederbaum",
"Carla",
""
],
[
"Cogo",
"Albachiara",
""
]
] | We study 4-dimensional asymptotically flat electrostatic electro-vacuum spacetimes with a connected black hole, photon sphere, or equipotential photon surface inner boundary. Our analysis, inspired by the potential theory approach by Agostiniani-Mazzieri, allows to give self-contained proofs of known uniqueness theorems of the sub-extremal, extremal and super-extremal Reissner-Nordstr\"om spacetimes. We also obtain new results for connected photon spheres and for connected photon surfaces in the extremal case. Finally, we provide, up to a restriction on the range of their radii, the uniqueness result for connected (both non-degenerate and degenerate) photon surfaces in the super-extremal case, not yet treated in the literature. |
1412.0105 | Samad Khakshournia | S. Khakshournia | A note on Pathria's model of the universe as a black hole | 5 pages | Grav.Cosmol.16:178-180,2010 | 10.1134/S0202289310020131 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Pathria has shown that for the certain values of the cosmological constant, a
pressureless closed Friedmann-Robertson-Walker universe can be the interior of
a Schwarzschild black hole. We examine the Pathria's model from the point of
view of the matching of the two different spacetimes through a null
hypersurface. We first regard the event horizon of the black hole, which in the
Pathria's model is identified with the radius of the universe at the point of
its maximum expansion, as a null hypersurface separating the FRW interior from
the vacuum Schwarzschild exterior, and then use the null shell formalism for
it. It turns out that the matching is not smooth, and in fact, the null
hypersurface is the history of a null shell admitting a surface pressure.
| [
{
"created": "Sat, 29 Nov 2014 13:31:15 GMT",
"version": "v1"
}
] | 2015-06-23 | [
[
"Khakshournia",
"S.",
""
]
] | Pathria has shown that for the certain values of the cosmological constant, a pressureless closed Friedmann-Robertson-Walker universe can be the interior of a Schwarzschild black hole. We examine the Pathria's model from the point of view of the matching of the two different spacetimes through a null hypersurface. We first regard the event horizon of the black hole, which in the Pathria's model is identified with the radius of the universe at the point of its maximum expansion, as a null hypersurface separating the FRW interior from the vacuum Schwarzschild exterior, and then use the null shell formalism for it. It turns out that the matching is not smooth, and in fact, the null hypersurface is the history of a null shell admitting a surface pressure. |
1704.03372 | Andr\'es Gomberoff | Claudio Bunster and Andr\'es Gomberoff | Gravitational domain walls and the dynamics of $G$ | 8 pages, 2 figures | Phys. Rev. D 96, 025013 (2017) | 10.1103/PhysRevD.96.025013 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | From the point of view of elementary particle physics the gravitational
constant $G$ is extraordinarily small. This has led to ask whether it could
have decayed to its present value from an initial one commensurate with
microscopical units. A mechanism that leads to such a decay is proposed herein.
It is based on assuming that $G$ may take different values within regions of
the universe separated by a novel kind of domain wall, a "G-wall". The idea is
implemented by introducing a gauge potential $A_{\mu\nu\rho}$, and its
conjugate $D$, which determines the value of $G$ as an integration constant
rather than a fundamental constant. The value of $G$ jumps when one goes
through a $G$-wall. The procedure extends one previously developed for the
cosmological constant, but the generalization is far from straightforward: (i)
The intrinsic geometry of a $G$-wall is not the same as seen from its two
sides, because the second law of black hole thermodynamics mandates that the
jump in $G$ must cause a discontinuity in the scale of length. (ii) The size of
the decay step in $G$ is controlled by a function $G(D)$ which may be chosen so
as to diminish the value of $G$ towards the asymptote $G=0$, without fine
tuning. It is shown that: (i) The dynamics of the gravitational field with $G$
treated as a dynamical variable, coupled to $G$-walls and matter, follows from
an action principle, which is given. (ii) A particle that impinges on a
$G$-wall may be refracted or reflected. (iii) The various forces between two
particles change when a $G$-wall is inserted in between them. (iv) $G$-walls
may be nucleated trough tunneling and thermal effects. The semiclassical
probabilities are evaluated. (v)~If the action principle is constructed
properly, the entropy of a black hole increases when the value of the
gravitational constant is changed through the absorption of a G-wall by the
hole.
| [
{
"created": "Tue, 11 Apr 2017 15:46:40 GMT",
"version": "v1"
}
] | 2017-07-26 | [
[
"Bunster",
"Claudio",
""
],
[
"Gomberoff",
"Andrés",
""
]
] | From the point of view of elementary particle physics the gravitational constant $G$ is extraordinarily small. This has led to ask whether it could have decayed to its present value from an initial one commensurate with microscopical units. A mechanism that leads to such a decay is proposed herein. It is based on assuming that $G$ may take different values within regions of the universe separated by a novel kind of domain wall, a "G-wall". The idea is implemented by introducing a gauge potential $A_{\mu\nu\rho}$, and its conjugate $D$, which determines the value of $G$ as an integration constant rather than a fundamental constant. The value of $G$ jumps when one goes through a $G$-wall. The procedure extends one previously developed for the cosmological constant, but the generalization is far from straightforward: (i) The intrinsic geometry of a $G$-wall is not the same as seen from its two sides, because the second law of black hole thermodynamics mandates that the jump in $G$ must cause a discontinuity in the scale of length. (ii) The size of the decay step in $G$ is controlled by a function $G(D)$ which may be chosen so as to diminish the value of $G$ towards the asymptote $G=0$, without fine tuning. It is shown that: (i) The dynamics of the gravitational field with $G$ treated as a dynamical variable, coupled to $G$-walls and matter, follows from an action principle, which is given. (ii) A particle that impinges on a $G$-wall may be refracted or reflected. (iii) The various forces between two particles change when a $G$-wall is inserted in between them. (iv) $G$-walls may be nucleated trough tunneling and thermal effects. The semiclassical probabilities are evaluated. (v)~If the action principle is constructed properly, the entropy of a black hole increases when the value of the gravitational constant is changed through the absorption of a G-wall by the hole. |
0812.4870 | Marie-Anne Bizouard | The Virgo Collaboration: F. Acernese, et al | Gravitational wave burst search in the Virgo C7 data | null | Class.Quant.Grav.26:085009,2009 | 10.1088/0264-9381/26/8/085009 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A search for gravitational wave burst events has been performed with the
Virgo C7 commissioning run data that have been acquired in September 2005 over
five days. It focused on un-modeled short duration signals in the frequency
range 150 Hz to 2 kHz. A search aimed at detecting the GW emission from the
merger and ringdown phases of binary black hole coalescences was also carried
out. An extensive understanding of the data was required to be able to handle a
burst search using the output of only one detector. A 90% confidence level
upper limit on the number of expected events given the Virgo C7 sensitivity
curve has been derived as a function of the signal strength, for un-modeled
gravitational wave search. The sensitivity of the analysis presented is, in
terms of the root sum square strain amplitude, $h_{rss} \simeq 10^{-20} /
\sqrt{Hz}$. This can be interpreted in terms of a frequentist upper limit on
the rate ${\cal{R}}_{90%}$ of detectable gravitational wave bursts at the level
of 1.1 events per day at 90% confidence level. From the binary black hole
search, we obtained the distance reach at 50% and 90% efficiency as a function
of the total mass of the final black hole. The maximal detection distance for
non-spinning high and equal mass black hole binary system obtained by this
analysis in C7 data is $\simeq$ 2.9 $\pm$ 0.1 Mpc for a detection efficiency of
50% for a binary of total mass $80 M_{\odot}$.
| [
{
"created": "Mon, 29 Dec 2008 04:22:02 GMT",
"version": "v1"
}
] | 2010-01-08 | [
[
"The Virgo Collaboration",
"",
""
],
[
"Acernese",
"F.",
""
]
] | A search for gravitational wave burst events has been performed with the Virgo C7 commissioning run data that have been acquired in September 2005 over five days. It focused on un-modeled short duration signals in the frequency range 150 Hz to 2 kHz. A search aimed at detecting the GW emission from the merger and ringdown phases of binary black hole coalescences was also carried out. An extensive understanding of the data was required to be able to handle a burst search using the output of only one detector. A 90% confidence level upper limit on the number of expected events given the Virgo C7 sensitivity curve has been derived as a function of the signal strength, for un-modeled gravitational wave search. The sensitivity of the analysis presented is, in terms of the root sum square strain amplitude, $h_{rss} \simeq 10^{-20} / \sqrt{Hz}$. This can be interpreted in terms of a frequentist upper limit on the rate ${\cal{R}}_{90%}$ of detectable gravitational wave bursts at the level of 1.1 events per day at 90% confidence level. From the binary black hole search, we obtained the distance reach at 50% and 90% efficiency as a function of the total mass of the final black hole. The maximal detection distance for non-spinning high and equal mass black hole binary system obtained by this analysis in C7 data is $\simeq$ 2.9 $\pm$ 0.1 Mpc for a detection efficiency of 50% for a binary of total mass $80 M_{\odot}$. |
1404.0589 | Gerard Clement | G\'erard Cl\'ement and Alessandro Fabbri | A scenario for critical scalar field collapse in $AdS_3$ | 19 pages, 3 figures, revised version to be published in Class. Quant.
Grav | Class. Quantum Grav. 32 (2015) 095009 | 10.1088/0264-9381/32/9/095009 | LAPTH-018/14 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a family of exact solutions, depending on two parameters $\alpha$
and $b$ (related to the scalar field strength), to the three-dimensional
Einstein-scalar field equations with negative cosmological constant $\Lambda$.
For $b=0$ these solutions reduce to the static BTZ family of vacuum solutions,
with mass $M = -\alpha$. For $b\neq0$, the solutions become dynamical and
develop a strong spacelike central singularity. The $\alpha<0$ solutions are
black-hole like, with a global structure topologically similar to that of the
BTZ black holes, and a finite effective mass. We show that the near-singularity
behavior of the solutions with $\alpha>0$ agrees qualitatively with that
observed in numerical simulations of subcritical collapse. We analyze the
linear perturbations of the threshold solution, $\alpha=0$, in the $\Lambda=0$
approximation, and find that it has only one unstable growing mode, which
qualifies it as a candidate critical solution for scalar field collapse.
| [
{
"created": "Wed, 2 Apr 2014 15:39:06 GMT",
"version": "v1"
},
{
"created": "Wed, 11 Mar 2015 18:46:53 GMT",
"version": "v2"
}
] | 2016-02-25 | [
[
"Clément",
"Gérard",
""
],
[
"Fabbri",
"Alessandro",
""
]
] | We present a family of exact solutions, depending on two parameters $\alpha$ and $b$ (related to the scalar field strength), to the three-dimensional Einstein-scalar field equations with negative cosmological constant $\Lambda$. For $b=0$ these solutions reduce to the static BTZ family of vacuum solutions, with mass $M = -\alpha$. For $b\neq0$, the solutions become dynamical and develop a strong spacelike central singularity. The $\alpha<0$ solutions are black-hole like, with a global structure topologically similar to that of the BTZ black holes, and a finite effective mass. We show that the near-singularity behavior of the solutions with $\alpha>0$ agrees qualitatively with that observed in numerical simulations of subcritical collapse. We analyze the linear perturbations of the threshold solution, $\alpha=0$, in the $\Lambda=0$ approximation, and find that it has only one unstable growing mode, which qualifies it as a candidate critical solution for scalar field collapse. |
0706.1157 | Albert V. Minkevich | A. V. Minkevich, A. S. Garkun and V. I. Kudin | Regular accelerating Universe without dark energy | 15 pages, 16 figures, iopart class file, some additions made | Class.Quant.Grav.24:5835-5848,2007 | 10.1088/0264-9381/24/23/007 | null | gr-qc | null | Homogeneous isotropic cosmological models with two torsion functions filled
with scalar fields and usual gravitating matter are built and investigated in
the framework of the Poincar\'e gauge theory of gravity. It is shown that by
certain restrictions on indefinite parameters of gravitational Lagrangian the
cosmological equations at asymptotics contain an effective cosmological
constant that can explain observable acceleration of cosmological expansion.
The behavior of inflationary cosmological solutions at extremely high energy
densities is analyzed, regular bouncing solutions are obtained. The role of the
space-time torsion provoking the acceleration of cosmological expansion is
discussed.
| [
{
"created": "Fri, 8 Jun 2007 11:06:49 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Oct 2007 07:27:28 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Minkevich",
"A. V.",
""
],
[
"Garkun",
"A. S.",
""
],
[
"Kudin",
"V. I.",
""
]
] | Homogeneous isotropic cosmological models with two torsion functions filled with scalar fields and usual gravitating matter are built and investigated in the framework of the Poincar\'e gauge theory of gravity. It is shown that by certain restrictions on indefinite parameters of gravitational Lagrangian the cosmological equations at asymptotics contain an effective cosmological constant that can explain observable acceleration of cosmological expansion. The behavior of inflationary cosmological solutions at extremely high energy densities is analyzed, regular bouncing solutions are obtained. The role of the space-time torsion provoking the acceleration of cosmological expansion is discussed. |
2308.02268 | Sergey Sushkov V | Valeria A. Ishkaeva, Sergey V. Sushkov | Image of an accreting general Ellis-Bronnikov wormhole | 11 pages, 6 figures, new references was added | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Gravitational lensing properties of supermassive astrophysical objects, such
as black holes and wormholes, provide the realistic way for their discovering
and investigating. Various lensing effects in a wormhole spacetime have been
widely studied in the literature. One of the most popular object for
investigation is the Ellis wormhole which represents the simplest wormhole
geometry. The Ellis solution represents only the particular case of a general
wormhole solution found independently by Ellis and Bronnikov. Surprisingly but
gravitational lensing properties of general Ellis-Bronnikov wormholes are
practically not investigated. In this paper we explore in details the
propagation of light, forming a shadow and silhouette, and forming an image of
accretion disk in the spacetime of the Ellis-Bronnikov wormhole. As well we
compare characteristics of images obtained for the Ellis-Bronnikov wormhole
with those for the Schwarzschild black hole. This comparison could be useful
for future observations of supermassive astrophysical objects.
| [
{
"created": "Fri, 4 Aug 2023 11:46:07 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Aug 2023 15:02:41 GMT",
"version": "v2"
}
] | 2023-08-10 | [
[
"Ishkaeva",
"Valeria A.",
""
],
[
"Sushkov",
"Sergey V.",
""
]
] | Gravitational lensing properties of supermassive astrophysical objects, such as black holes and wormholes, provide the realistic way for their discovering and investigating. Various lensing effects in a wormhole spacetime have been widely studied in the literature. One of the most popular object for investigation is the Ellis wormhole which represents the simplest wormhole geometry. The Ellis solution represents only the particular case of a general wormhole solution found independently by Ellis and Bronnikov. Surprisingly but gravitational lensing properties of general Ellis-Bronnikov wormholes are practically not investigated. In this paper we explore in details the propagation of light, forming a shadow and silhouette, and forming an image of accretion disk in the spacetime of the Ellis-Bronnikov wormhole. As well we compare characteristics of images obtained for the Ellis-Bronnikov wormhole with those for the Schwarzschild black hole. This comparison could be useful for future observations of supermassive astrophysical objects. |
1211.0200 | Yury F. Pirogov | Yu. F. Pirogov | Unimodular bimode gravity, grand unification and the scalar-graviton
dark matter | 4 pages | null | null | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In prior article of the author, the unimodular bimode gravity/systo-gravity,
with the scalar-graviton/systolon dark matter, was worked out. To compile with
the anomalous rotation curves of galaxies the scale of the local scale
violation in the theory was shown to be about 10^15 GeV. In this letter, to
naturally incorporate such a scale the hyper unification framework, merging
systo-gravity with grand unification through matter, is constructed. The
systolon, as a free propagating compression mode in metric, emerges only below
the unification scale, possessing at the same time a modified high-energy
behavior to be manifested at the high temperatures.
| [
{
"created": "Thu, 1 Nov 2012 15:12:23 GMT",
"version": "v1"
}
] | 2012-11-02 | [
[
"Pirogov",
"Yu. F.",
""
]
] | In prior article of the author, the unimodular bimode gravity/systo-gravity, with the scalar-graviton/systolon dark matter, was worked out. To compile with the anomalous rotation curves of galaxies the scale of the local scale violation in the theory was shown to be about 10^15 GeV. In this letter, to naturally incorporate such a scale the hyper unification framework, merging systo-gravity with grand unification through matter, is constructed. The systolon, as a free propagating compression mode in metric, emerges only below the unification scale, possessing at the same time a modified high-energy behavior to be manifested at the high temperatures. |
gr-qc/9308015 | null | Arlen Anderson | The use of exp(iS[x]) in the sum over histories | 22 pages, Latex, Imperial-TP-92-93-46 | Phys.Rev. D49 (1994) 4049-4055 | 10.1103/PhysRevD.49.4049 | null | gr-qc hep-th | null | The use of $\sum \exp(iS[x])$ as the generic form for a sum over histories in
configuration space is discussed critically and placed in its proper context.
The standard derivation of the sum over paths by discretizing the paths is
reviewed, and it is shown that the form $\sum \exp(iS[x])$ is justified only
for Schrodinger-type systems which are at most second order in the momenta.
Extending this derivation to the relativistic free particle, the causal Green's
function is expressed as a sum over timelike paths, and the Feynman Green's
function is expressed both as a sum over paths which only go one way in time
and as a sum over paths which move forward and backward in time. The weighting
of the paths is shown not to be $\exp(iS[x])$ in any of these cases. The role
of the inner product and the operator ordering of the wave equation in defining
the sum over histories is discussed.
| [
{
"created": "Tue, 17 Aug 1993 08:40:43 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Anderson",
"Arlen",
""
]
] | The use of $\sum \exp(iS[x])$ as the generic form for a sum over histories in configuration space is discussed critically and placed in its proper context. The standard derivation of the sum over paths by discretizing the paths is reviewed, and it is shown that the form $\sum \exp(iS[x])$ is justified only for Schrodinger-type systems which are at most second order in the momenta. Extending this derivation to the relativistic free particle, the causal Green's function is expressed as a sum over timelike paths, and the Feynman Green's function is expressed both as a sum over paths which only go one way in time and as a sum over paths which move forward and backward in time. The weighting of the paths is shown not to be $\exp(iS[x])$ in any of these cases. The role of the inner product and the operator ordering of the wave equation in defining the sum over histories is discussed. |
1711.10256 | Cosimo Bambi | Cosimo Bambi | Astrophysical Black Holes: A Compact Pedagogical Review | 17 pages, 8 figures. v3: refereed version | Annalen der Physik 530, 1700430 (2018) | 10.1002/andp.201700430 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black holes are among the most extreme objects that can be found in the
Universe and an ideal laboratory for testing fundamental physics. This article
will briefly review the basic properties of black holes as expected from
general relativity, the main astronomical observations, and the leading
astrophysical techniques to probe the strong gravity region of these objects.
It is mainly intended to provide a compact introductory overview on
astrophysical black holes to new students entering this research field, as well
as to senior researchers working in general relativity and alternative theories
of gravity and wishing to quickly learn the state of the art of astronomical
observations of black holes.
| [
{
"created": "Tue, 28 Nov 2017 12:40:40 GMT",
"version": "v1"
},
{
"created": "Sun, 21 Jan 2018 12:21:15 GMT",
"version": "v2"
},
{
"created": "Wed, 31 Jan 2018 22:47:02 GMT",
"version": "v3"
}
] | 2018-05-07 | [
[
"Bambi",
"Cosimo",
""
]
] | Black holes are among the most extreme objects that can be found in the Universe and an ideal laboratory for testing fundamental physics. This article will briefly review the basic properties of black holes as expected from general relativity, the main astronomical observations, and the leading astrophysical techniques to probe the strong gravity region of these objects. It is mainly intended to provide a compact introductory overview on astrophysical black holes to new students entering this research field, as well as to senior researchers working in general relativity and alternative theories of gravity and wishing to quickly learn the state of the art of astronomical observations of black holes. |
0712.2593 | Pouria Pedram | P. Pedram, S. Jalalzadeh | Quantum cosmology with varying speed of light: canonical approach | 14 pages, 7 figures, to appear in Physics Letters B | Phys.Lett.B660:1-6,2008 | 10.1016/j.physletb.2007.11.098 | null | gr-qc | null | We investigate $(n+1)$--dimensional cosmology with varying speed of light.
After solving corresponding Wheeler-DeWitt equation, we obtain exact solutions
in both classical and quantum levels for ($c $--$\Lambda$)--dominated Universe.
We then construct the ``canonical'' wave packets which exhibit a good classical
and quantum correspondence. We show that arbitrary but appropriate initial
conditions lead to the same classical description. We also study the situation
from de-Broglie Bohm interpretation of quantum mechanics and show that the
corresponding Bohmian trajectories are in good agreement with the classical
counterparts.
| [
{
"created": "Sun, 16 Dec 2007 20:48:44 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Pedram",
"P.",
""
],
[
"Jalalzadeh",
"S.",
""
]
] | We investigate $(n+1)$--dimensional cosmology with varying speed of light. After solving corresponding Wheeler-DeWitt equation, we obtain exact solutions in both classical and quantum levels for ($c $--$\Lambda$)--dominated Universe. We then construct the ``canonical'' wave packets which exhibit a good classical and quantum correspondence. We show that arbitrary but appropriate initial conditions lead to the same classical description. We also study the situation from de-Broglie Bohm interpretation of quantum mechanics and show that the corresponding Bohmian trajectories are in good agreement with the classical counterparts. |
1108.3003 | Burkhard Kleihaus | Panagiota Kanti, Burkhard Kleihaus, Jutta Kunz | Wormholes in Dilatonic Einstein-Gauss-Bonnet Theory | updated version, published in PRL | Phys.Rev.Lett. 107 (2011) 271101 | 10.1103/PhysRevLett.107.271101 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct traversable wormholes in dilatonic Einstein-Gauss-Bonnet theory
in four spacetime dimensions, without needing any form of exotic matter. We
determine their domain of existence, and show that these wormholes satisfy a
generalised Smarr relation. We demonstrate linear stability with respect to
radial perturbations for a subset of these wormholes.
| [
{
"created": "Mon, 15 Aug 2011 14:17:16 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Mar 2012 10:10:07 GMT",
"version": "v2"
}
] | 2015-05-30 | [
[
"Kanti",
"Panagiota",
""
],
[
"Kleihaus",
"Burkhard",
""
],
[
"Kunz",
"Jutta",
""
]
] | We construct traversable wormholes in dilatonic Einstein-Gauss-Bonnet theory in four spacetime dimensions, without needing any form of exotic matter. We determine their domain of existence, and show that these wormholes satisfy a generalised Smarr relation. We demonstrate linear stability with respect to radial perturbations for a subset of these wormholes. |
gr-qc/0204039 | Maeda Hideki | Hideki Maeda, Tomohiro Harada, Hideo Iguchi and Naoya Okuyama | No Go Theorem for Kinematic Self-Similarity with A Polytropic Equation
of State | 5 pages, no figures. Revtex. One word added to the title. Final
version to appear in Physical Review D as a Brief Report | Phys.Rev. D66 (2002) 027501 | 10.1103/PhysRevD.66.027501 | WU-AP/143/02 | gr-qc | null | We have investigated spherically symmetric spacetimes which contain a perfect
fluid obeying the polytropic equation of state and admit a kinematic
self-similar vector of the second kind which is neither parallel nor orthogonal
to the fluid flow. We have assumed two kinds of polytropic equations of state
and shown in general relativity that such spacetimes must be vacuum.
| [
{
"created": "Wed, 10 Apr 2002 08:15:24 GMT",
"version": "v1"
},
{
"created": "Sat, 25 May 2002 21:09:32 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Maeda",
"Hideki",
""
],
[
"Harada",
"Tomohiro",
""
],
[
"Iguchi",
"Hideo",
""
],
[
"Okuyama",
"Naoya",
""
]
] | We have investigated spherically symmetric spacetimes which contain a perfect fluid obeying the polytropic equation of state and admit a kinematic self-similar vector of the second kind which is neither parallel nor orthogonal to the fluid flow. We have assumed two kinds of polytropic equations of state and shown in general relativity that such spacetimes must be vacuum. |
gr-qc/9511079 | null | B. L. Hu | Statistical Mechanics and Quantum Cosmology | Essay published in 1990 Conference Proceedings is reprinted here with
no alteration nor reference update. It is antecedent to related reviews in
gr-qc/9302025, gr-qc/9403061, gr-qc/9511077 | null | null | University of Maryland Physics Preprint UMDPP 91-096 | gr-qc | null | Statistical mechanical concepts and processes such as decoherence,
correlation, and dissipation can prove to be of basic importance to
understanding some fundamental issues of quantum cosmology and theoretical
physics such as the choice of initial states, quantum to classical transition
and the emergence of time. Here we summarize our effort in 1) constructing a
unified theoretical framework using techniques in interacting quantum field
theory such as influence functional and coarse-grained effective action to
discuss the interplay of noise, fluctuation, dissipation and decoherence; and
2) illustrating how these concepts when applied to quantum cosmology can alter
the conventional views on some basic issues. Two questions we address are 1)
the validity of minisuperspace truncation, which is usually assumed without
proof in most discussions, and 2) the relevance of specific initial conditions,
which is the prevailing view of the past decade. We also mention how some
current ideas in chaotic dynamics, dissipative collective dynamics and
complexity can alter our view of the quantum nature of the universe.
| [
{
"created": "Wed, 29 Nov 1995 03:42:33 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Hu",
"B. L.",
""
]
] | Statistical mechanical concepts and processes such as decoherence, correlation, and dissipation can prove to be of basic importance to understanding some fundamental issues of quantum cosmology and theoretical physics such as the choice of initial states, quantum to classical transition and the emergence of time. Here we summarize our effort in 1) constructing a unified theoretical framework using techniques in interacting quantum field theory such as influence functional and coarse-grained effective action to discuss the interplay of noise, fluctuation, dissipation and decoherence; and 2) illustrating how these concepts when applied to quantum cosmology can alter the conventional views on some basic issues. Two questions we address are 1) the validity of minisuperspace truncation, which is usually assumed without proof in most discussions, and 2) the relevance of specific initial conditions, which is the prevailing view of the past decade. We also mention how some current ideas in chaotic dynamics, dissipative collective dynamics and complexity can alter our view of the quantum nature of the universe. |
1209.4842 | Giulio Caciotta | Giulio Caciotta and Tiziana Raparelli | Asymptotic Behaviour of Zero Mass spin 2 Fields propagating in the
external region of Kerr spacetime | 61 pages, no figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | After describing the inhomogeneous equation suitable to describe
W{\nu}{\mu}{\rho}{\sigma}, a solution of the linearized version of the full
quasilinear equation for the conformal part of the Riemann tensor connected to
the perturbations of the Kerr spacetime far from the origin, we find the right
decays we have to impose to the source term to obtain the peeling decays for
this linearized solution. We basically follow the ideas of the Christodoulou
Klainerman approach, [Ch-Kl] and [Kl-Ni1]. This result requires some new
detailed estimates which could be considered a useful result by themselves.
| [
{
"created": "Fri, 21 Sep 2012 15:16:29 GMT",
"version": "v1"
}
] | 2012-09-24 | [
[
"Caciotta",
"Giulio",
""
],
[
"Raparelli",
"Tiziana",
""
]
] | After describing the inhomogeneous equation suitable to describe W{\nu}{\mu}{\rho}{\sigma}, a solution of the linearized version of the full quasilinear equation for the conformal part of the Riemann tensor connected to the perturbations of the Kerr spacetime far from the origin, we find the right decays we have to impose to the source term to obtain the peeling decays for this linearized solution. We basically follow the ideas of the Christodoulou Klainerman approach, [Ch-Kl] and [Kl-Ni1]. This result requires some new detailed estimates which could be considered a useful result by themselves. |
2302.03612 | Waleed Sherif | Hanno Sahlmann and Waleed Sherif | A Fock space structure for the diffeomorphism invariant Hilbert space of
loop quantum gravity and its applications | 26 pages, 5 figures | null | null | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Loop quantum gravity (LQG) is a quantization program for gravity based on the
principles of QFT and general covariance of general relativity. Quantum states
of LQG describe gravitational excitations based on graphs embedded in a spatial
slice of spacetime. We show that, under certain assumptions on the class of
diffeomorphisms, the space of diffeomorphism invariant states carries a Fock
space structure. The role of one-particle excitations for this structure is
played by the diffeomorphism invariant states based on graphs with a single
(linked) component. This means, however, that a lot of the structure of the
diffeomorphism invariant Hilbert space remains unresolved by this structure. We
show how the Fock structure allows to write at least some condensate states of
group field theory as diffeomorphism invariant coherent states of LQG in a
precise sense. We also show how to construct other interesting states using
this Fock structure. We finally explore the quantum geometry of single- and
multi-particle states and tentatively observe some resemblance to geometries
with a single or multiple components, respectively.
| [
{
"created": "Tue, 7 Feb 2023 17:15:39 GMT",
"version": "v1"
}
] | 2023-02-08 | [
[
"Sahlmann",
"Hanno",
""
],
[
"Sherif",
"Waleed",
""
]
] | Loop quantum gravity (LQG) is a quantization program for gravity based on the principles of QFT and general covariance of general relativity. Quantum states of LQG describe gravitational excitations based on graphs embedded in a spatial slice of spacetime. We show that, under certain assumptions on the class of diffeomorphisms, the space of diffeomorphism invariant states carries a Fock space structure. The role of one-particle excitations for this structure is played by the diffeomorphism invariant states based on graphs with a single (linked) component. This means, however, that a lot of the structure of the diffeomorphism invariant Hilbert space remains unresolved by this structure. We show how the Fock structure allows to write at least some condensate states of group field theory as diffeomorphism invariant coherent states of LQG in a precise sense. We also show how to construct other interesting states using this Fock structure. We finally explore the quantum geometry of single- and multi-particle states and tentatively observe some resemblance to geometries with a single or multiple components, respectively. |
1701.02703 | Killian Martineau | Killian Martineau, Aur\'elien Barrau and Susanne Schander | Detailed investigation of the duration of inflation in loop quantum
cosmology for a Bianchi-I universe with different inflaton potentials and
initial conditions | null | Phys. Rev. D 95, 083507 (2017) | 10.1103/PhysRevD.95.083507 | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There is a wide consensus on the correct dynamics of the background in loop
quantum cosmology. In this article we make a systematic investigation of the
duration of inflation by varying what we think to be the most important
"unknowns" of the model: the way to set initial conditions, the amount of shear
at the bounce and the shape of the inflaton potential.
| [
{
"created": "Tue, 10 Jan 2017 17:43:09 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Mar 2017 15:00:33 GMT",
"version": "v2"
}
] | 2017-04-19 | [
[
"Martineau",
"Killian",
""
],
[
"Barrau",
"Aurélien",
""
],
[
"Schander",
"Susanne",
""
]
] | There is a wide consensus on the correct dynamics of the background in loop quantum cosmology. In this article we make a systematic investigation of the duration of inflation by varying what we think to be the most important "unknowns" of the model: the way to set initial conditions, the amount of shear at the bounce and the shape of the inflaton potential. |
gr-qc/9809036 | Takashi. Torii | T. Torii, K. Meeda and M. Narita | No-scalar hair conjecture in asymptotic de-Sitter spacetime | 9 pages, 2 Postscript figures | Phys.Rev. D59 (1999) 064027 | 10.1103/PhysRevD.59.064027 | Tokyo Institute of Technology preprint TIT/HEP-403 | gr-qc | null | We discuss the no-hair conjecture in the presence of a cosmological constant.
For the firststep the real scalar field is considered as the matter field and
the spacetime is assumed to be static spherically symmetric. If the scalar
field is massless or has a convex potential such as a mass term, it is proved
that there is no regular black hole solution. For a general positive potential,
we search for black hole solutions which support the scalar field with a double
well potential, and find them by numerical calculations. The existence of such
solutions depends on the values of the vacuum expectation value and the
self-coupling constant of the scalar field. When we take the zero horizon
radius limit, the solution becomes a boson star like solution which we found
before. However new solutions are found to be unstable against the linear
perturbation. As a result we can conclude that the no-scalar hair conjecture
holds in the case of scalar fields with a convex or double well potential.
| [
{
"created": "Wed, 9 Sep 1998 12:42:17 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Torii",
"T.",
""
],
[
"Meeda",
"K.",
""
],
[
"Narita",
"M.",
""
]
] | We discuss the no-hair conjecture in the presence of a cosmological constant. For the firststep the real scalar field is considered as the matter field and the spacetime is assumed to be static spherically symmetric. If the scalar field is massless or has a convex potential such as a mass term, it is proved that there is no regular black hole solution. For a general positive potential, we search for black hole solutions which support the scalar field with a double well potential, and find them by numerical calculations. The existence of such solutions depends on the values of the vacuum expectation value and the self-coupling constant of the scalar field. When we take the zero horizon radius limit, the solution becomes a boson star like solution which we found before. However new solutions are found to be unstable against the linear perturbation. As a result we can conclude that the no-scalar hair conjecture holds in the case of scalar fields with a convex or double well potential. |
1808.07988 | Yan Peng | Yan Peng | Hair distributions in noncommutative Einstein-Born-Infeld black holes | 11 pages, 4 figures | Nuclear Physics B 941(2019)1-10 | 10.1016/j.nuclphysb.2019.02.016 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study hair mass distributions in noncommutative Einstein-Born-Infeld hairy
black holes with non-zero cosmological constants. We find that the larger
noncommutative parameter makes the hair easier to condense in the near horizon
area. We also show that Hod's lower bound can be evaded in the noncommutative
gravity. However, for large black holes with a non-negative cosmological
constant, Hod's lower hair mass bound almost holds in the sense that nearly
half of the hair lays above the photonsphere.
| [
{
"created": "Fri, 24 Aug 2018 02:57:55 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Feb 2019 02:07:55 GMT",
"version": "v2"
}
] | 2019-02-25 | [
[
"Peng",
"Yan",
""
]
] | We study hair mass distributions in noncommutative Einstein-Born-Infeld hairy black holes with non-zero cosmological constants. We find that the larger noncommutative parameter makes the hair easier to condense in the near horizon area. We also show that Hod's lower bound can be evaded in the noncommutative gravity. However, for large black holes with a non-negative cosmological constant, Hod's lower hair mass bound almost holds in the sense that nearly half of the hair lays above the photonsphere. |
2212.00164 | Gines Perez Teruel | Gin\'es R. P\'erez Teruel, Ksh. Newton Singh, Farook Rahaman, Tanmoy
Chowdhury | Possible existence of stable compact stars in
$\kappa(\mathcal{R},\mathcal{T})-$gravity | 15 pages, 9 figures | null | 10.1142/S0217751X22501949 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We present the first interior solutions representing compact stars in
$\kappa(\mathcal{R},\mathcal{T})$ gravity, by solving the modified field
equations in isotropic coordinates. Further, we have assumed the metric
potentials in Schwarzschild's form and a few parameters along with the
isotropic condition of pressure. For solving, we use specific choice of the
running gravitational constant as $\kappa(\mathcal{R},\mathcal{T})=8\pi-\lambda
\mathcal{T} ~~(G=\tilde{c}=1)$. Once arrived at the reduced field equations, we
investigate two solutions with $c=1$ and $c \neq 1$, where $c$ denotes here
another constant that should not be confused with the speed of light. Then, we
investigate each solution by determining the thermodynamics variable {\it viz}
pressure, density, speed of sound, and adiabatic index. We found that these
solutions satisfy the Bondi criterion, causality condition, and energy
conditions. We also found that the $M-R$ curves generated from these solutions
satisfy the stringent constraints provided by the gravitational wave
observations due to the neutron star merger GW 170817.
| [
{
"created": "Wed, 30 Nov 2022 23:25:53 GMT",
"version": "v1"
}
] | 2022-12-02 | [
[
"Teruel",
"Ginés R. Pérez",
""
],
[
"Singh",
"Ksh. Newton",
""
],
[
"Rahaman",
"Farook",
""
],
[
"Chowdhury",
"Tanmoy",
""
]
] | We present the first interior solutions representing compact stars in $\kappa(\mathcal{R},\mathcal{T})$ gravity, by solving the modified field equations in isotropic coordinates. Further, we have assumed the metric potentials in Schwarzschild's form and a few parameters along with the isotropic condition of pressure. For solving, we use specific choice of the running gravitational constant as $\kappa(\mathcal{R},\mathcal{T})=8\pi-\lambda \mathcal{T} ~~(G=\tilde{c}=1)$. Once arrived at the reduced field equations, we investigate two solutions with $c=1$ and $c \neq 1$, where $c$ denotes here another constant that should not be confused with the speed of light. Then, we investigate each solution by determining the thermodynamics variable {\it viz} pressure, density, speed of sound, and adiabatic index. We found that these solutions satisfy the Bondi criterion, causality condition, and energy conditions. We also found that the $M-R$ curves generated from these solutions satisfy the stringent constraints provided by the gravitational wave observations due to the neutron star merger GW 170817. |
0712.2667 | Yuri Pavlov | A. A. Grib and Yu. V. Pavlov | Do active galactic nuclei convert dark matter into visible particles? | LATEX, 5 pages, no figure | Mod.Phys.Lett.A23:1151-1159,2008 | 10.1142/S0217732308027072 | null | gr-qc astro-ph hep-ph | null | The hypothesis that dark matter consists of superheavy particles with the
mass close to the Grand Unification scale is investigated. These particles were
created from vacuum by the gravitation of the expanding Universe and their
decay led to the observable baryon charge. Some part of these particles with
the lifetime larger than the time of breaking of the Grand Unification symmetry
became metastable and survived up to the modern time as dark matter. However in
active galactic nuclei due to large energies of dark matter particles swallowed
by the black hole the opposite process can occur. Dark matter particles become
interacting. Their decay on visible particles at the Grand Unification energies
leads to the flow of ultra high energy cosmic rays observed by the Auger group.
Numerical estimates of the effect leading to the observable numbers are given.
| [
{
"created": "Mon, 17 Dec 2007 09:51:10 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Grib",
"A. A.",
""
],
[
"Pavlov",
"Yu. V.",
""
]
] | The hypothesis that dark matter consists of superheavy particles with the mass close to the Grand Unification scale is investigated. These particles were created from vacuum by the gravitation of the expanding Universe and their decay led to the observable baryon charge. Some part of these particles with the lifetime larger than the time of breaking of the Grand Unification symmetry became metastable and survived up to the modern time as dark matter. However in active galactic nuclei due to large energies of dark matter particles swallowed by the black hole the opposite process can occur. Dark matter particles become interacting. Their decay on visible particles at the Grand Unification energies leads to the flow of ultra high energy cosmic rays observed by the Auger group. Numerical estimates of the effect leading to the observable numbers are given. |
gr-qc/9909023 | Valery M. Koryukin | Valery Koryukin (Mari State Technical University) | New methods in the theory of gauge fields | 13 pages, submitted to Physical Review D | null | null | null | gr-qc | null | One of the fundamental problems of the theoretical physics is the search of
the axioms, which ought to be the basis for the one-valued construction of
Lagrangians of the relativistic fields. The creation of the gauge fields theory
was the great success in the solution of this problem. The gauge formalism
allowed to derive the total Lagrangians of the interacting fields from the
postulated Lagrangians of the noninteracting (free) fields. We offer to do
quite the reverse in consequence of what it is necessary to seek from the out
set the construction principles of the total Lagrangians. By the theory
construction we shall differ the wave-functions being the solutions of the
differential equations (``theoretical'' functions) from the wave-functions
which is constructed on the base of the experimental data possibly received by
a scattering of particles (``empiric'' functions). The ``empiric'' functions
are necessary only for the definition (it is possibly only approximately) of
the transition operators which will affect at the ``theoretical'' functions.
This operators will be approximated the differential operators so, that the
generalized variance of the differentiable
``theoretical'' fields will be the minimal one.
| [
{
"created": "Tue, 7 Sep 1999 06:40:16 GMT",
"version": "v1"
},
{
"created": "Mon, 24 Jan 2000 16:55:00 GMT",
"version": "v2"
}
] | 2016-08-31 | [
[
"Koryukin",
"Valery",
"",
"Mari State Technical University"
]
] | One of the fundamental problems of the theoretical physics is the search of the axioms, which ought to be the basis for the one-valued construction of Lagrangians of the relativistic fields. The creation of the gauge fields theory was the great success in the solution of this problem. The gauge formalism allowed to derive the total Lagrangians of the interacting fields from the postulated Lagrangians of the noninteracting (free) fields. We offer to do quite the reverse in consequence of what it is necessary to seek from the out set the construction principles of the total Lagrangians. By the theory construction we shall differ the wave-functions being the solutions of the differential equations (``theoretical'' functions) from the wave-functions which is constructed on the base of the experimental data possibly received by a scattering of particles (``empiric'' functions). The ``empiric'' functions are necessary only for the definition (it is possibly only approximately) of the transition operators which will affect at the ``theoretical'' functions. This operators will be approximated the differential operators so, that the generalized variance of the differentiable ``theoretical'' fields will be the minimal one. |
2401.10479 | Roberto A. Sussman | Roberto A Sussman, Carlo Alberto Mantica, Luca Guido Molinari and
Sebasti\'an N\'ajera | Response to a critique of "Cotton Gravity" | Important corrections and extra arguments added. 5 pages, all typos
corrected | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | We address in this article the criticism in a recently submitted article by
Clement and Noiucer (arXiv:2312.17662 [gr-qc]) on "Cotton Gravity" (CG), a
gravity theory alternative to General Relativity. These authors claim that CG
is "not predictive" for producing "too many" spherically symmetric vacuum
solutions, while taking the Bianchi I vacuum as test case they argue that
geometric constraint on the Cotton tensor lead to an undetermined problem,
concluding in the end that CG "is not a physical theory". We provide arguments
showing that this critique is incorrect and misrepresents the theory.
| [
{
"created": "Fri, 19 Jan 2024 04:03:31 GMT",
"version": "v1"
},
{
"created": "Tue, 23 Jan 2024 19:51:47 GMT",
"version": "v2"
}
] | 2024-01-25 | [
[
"Sussman",
"Roberto A",
""
],
[
"Mantica",
"Carlo Alberto",
""
],
[
"Molinari",
"Luca Guido",
""
],
[
"Nájera",
"Sebastián",
""
]
] | We address in this article the criticism in a recently submitted article by Clement and Noiucer (arXiv:2312.17662 [gr-qc]) on "Cotton Gravity" (CG), a gravity theory alternative to General Relativity. These authors claim that CG is "not predictive" for producing "too many" spherically symmetric vacuum solutions, while taking the Bianchi I vacuum as test case they argue that geometric constraint on the Cotton tensor lead to an undetermined problem, concluding in the end that CG "is not a physical theory". We provide arguments showing that this critique is incorrect and misrepresents the theory. |
2111.06561 | Rui Xu | Rui Xu, Yong Gao, and Lijing Shao | Neutron stars in massive scalar-Gauss-Bonnet gravity: Spherical
structure and time-independent perturbations | 21 pages, 9 figures | Phys. Rev. D 105, 024003 (2022) | 10.1103/PhysRevD.105.024003 | null | gr-qc physics.comp-ph | http://creativecommons.org/licenses/by-sa/4.0/ | The class of scalar-tensor theories with the scalar field coupling to the
Gauss-Bonnet invariant has drawn great interest since solutions of spontaneous
scalarization were found for black holes in these theories. We contribute to
the existing literature a detailed study of the spontaneously scalarized
neutron stars (NSs) in a typical theory where the coupling function of the
scalar field takes the quadratic form and the scalar field is massive. The
investigation here includes the spherical solutions of the NSs as well as their
perturbative properties, namely the tidal deformability and the moment of
inertia, treated in a unified and extendable way under the framework of
spherical decomposition. We find that while the mass, the radius, and the
moment of inertia of the spontaneously scalarized NSs show very moderate
deviations from those of the NSs in general relativity (GR), the tidal
deformability exhibits significant differences between the solutions in GR and
the solutions of spontaneous scalarization for certain values of the parameters
in the scalar-Gauss-Bonnet theory. As a result, the celebrated universal
relation between the moment of inertia and the tidal deformability of neutron
stars breaks down. With the mass and the tidal deformability of NSs attainable
in the gravitational waves from binary NS mergers, the radius measurable using
the X-ray satellites, and the moment of inertia accessible via the
high-precision pulsar timing techniques, future multi-messenger observations
can be contrasted with the theoretical results and provide us necessary
information for building up theories beyond GR.
| [
{
"created": "Fri, 12 Nov 2021 04:29:47 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Dec 2021 04:33:29 GMT",
"version": "v2"
}
] | 2022-01-05 | [
[
"Xu",
"Rui",
""
],
[
"Gao",
"Yong",
""
],
[
"Shao",
"Lijing",
""
]
] | The class of scalar-tensor theories with the scalar field coupling to the Gauss-Bonnet invariant has drawn great interest since solutions of spontaneous scalarization were found for black holes in these theories. We contribute to the existing literature a detailed study of the spontaneously scalarized neutron stars (NSs) in a typical theory where the coupling function of the scalar field takes the quadratic form and the scalar field is massive. The investigation here includes the spherical solutions of the NSs as well as their perturbative properties, namely the tidal deformability and the moment of inertia, treated in a unified and extendable way under the framework of spherical decomposition. We find that while the mass, the radius, and the moment of inertia of the spontaneously scalarized NSs show very moderate deviations from those of the NSs in general relativity (GR), the tidal deformability exhibits significant differences between the solutions in GR and the solutions of spontaneous scalarization for certain values of the parameters in the scalar-Gauss-Bonnet theory. As a result, the celebrated universal relation between the moment of inertia and the tidal deformability of neutron stars breaks down. With the mass and the tidal deformability of NSs attainable in the gravitational waves from binary NS mergers, the radius measurable using the X-ray satellites, and the moment of inertia accessible via the high-precision pulsar timing techniques, future multi-messenger observations can be contrasted with the theoretical results and provide us necessary information for building up theories beyond GR. |
1809.01458 | Robert van den Hoogen | R. J. van den Hoogen, A. A. Coley, B. Alhulaimi, S. Mohandas, E.
Knighton, and S. O'Neil | Kantowski-Sachs Einstein-Aether Scalar Field Cosmological Models | 28 pages, 10 figures, 3 tables, submitted to JCAP | 2018 J. Cosmol. Astropart. Phys. 2018 017 | 10.1088/1475-7516/2018/11/017 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A class of positive curvature spatially homogeneous but anisotropic
cosmological models within an Einstein-aether gravitational framework are
investigated. The matter source is assumed to be a scalar field which is
coupled to the expansion of the aether field through a generalized exponential
potential. The evolution equations are expressed in terms of
expansion-normalized variables to produce an autonomous system of ordinary
differential equations suitable for a numerical and qualitative analysis. An
analysis of the local stability of the equilibrium points indicates that there
exists a range of values of the parameters in which there exists an
accelerating expansionary future attractor. In general relativity, scalar field
models with an exponential potential $V=V_0e^{-2k\phi}$ have a late-time
inflationary attractor for $k^2<\frac{1}{2}$; however, it is found that the
existence of the coupling between the aether and scalar fields allows for
arbitrarily large values of the parameter $k$.
| [
{
"created": "Wed, 5 Sep 2018 12:39:07 GMT",
"version": "v1"
}
] | 2019-03-27 | [
[
"Hoogen",
"R. J. van den",
""
],
[
"Coley",
"A. A.",
""
],
[
"Alhulaimi",
"B.",
""
],
[
"Mohandas",
"S.",
""
],
[
"Knighton",
"E.",
""
],
[
"O'Neil",
"S.",
""
]
] | A class of positive curvature spatially homogeneous but anisotropic cosmological models within an Einstein-aether gravitational framework are investigated. The matter source is assumed to be a scalar field which is coupled to the expansion of the aether field through a generalized exponential potential. The evolution equations are expressed in terms of expansion-normalized variables to produce an autonomous system of ordinary differential equations suitable for a numerical and qualitative analysis. An analysis of the local stability of the equilibrium points indicates that there exists a range of values of the parameters in which there exists an accelerating expansionary future attractor. In general relativity, scalar field models with an exponential potential $V=V_0e^{-2k\phi}$ have a late-time inflationary attractor for $k^2<\frac{1}{2}$; however, it is found that the existence of the coupling between the aether and scalar fields allows for arbitrarily large values of the parameter $k$. |
2012.03260 | Xuefeng Zhang | Bo-Bing Ye, Xuefeng Zhang, Ming-Yue Zhou, Yan Wang, Hui-Min Yuan,
Defeng Gu, Yanwei Ding, Jinxiu Zhang, Jianwei Mei, Jun Luo | Optimizing orbits for TianQin | null | Int. J. Mod. Phys. D 28, 09, 1950121 (2019) | 10.1142/S0218271819501219 | null | gr-qc astro-ph.IM | http://creativecommons.org/licenses/by/4.0/ | TianQin is a geocentric space-based gravitational-wave observatory mission
consisting of three drag-free controlled satellites in an equilateral triangle
with an orbital radius of $ 10^{5}$ km. The constellation faces the white-dwarf
binary RX J0806.3+1527 located slightly below the ecliptic plane, and is
subject to gravitational perturbations that can distort the formation. In this
study, we present combined methods to optimize the TianQin orbits so that a set
of 5-year stability requirements can be met. Moreover, we discuss slow
long-term drift of the detector pointing due to orbital precession, and put
forward stable orbits with six other pointings along the lunar orbital plane.
Some implications of the findings are pointed out.
| [
{
"created": "Sun, 6 Dec 2020 13:26:21 GMT",
"version": "v1"
}
] | 2021-02-17 | [
[
"Ye",
"Bo-Bing",
""
],
[
"Zhang",
"Xuefeng",
""
],
[
"Zhou",
"Ming-Yue",
""
],
[
"Wang",
"Yan",
""
],
[
"Yuan",
"Hui-Min",
""
],
[
"Gu",
"Defeng",
""
],
[
"Ding",
"Yanwei",
""
],
[
"Zhang",
"Jin... | TianQin is a geocentric space-based gravitational-wave observatory mission consisting of three drag-free controlled satellites in an equilateral triangle with an orbital radius of $ 10^{5}$ km. The constellation faces the white-dwarf binary RX J0806.3+1527 located slightly below the ecliptic plane, and is subject to gravitational perturbations that can distort the formation. In this study, we present combined methods to optimize the TianQin orbits so that a set of 5-year stability requirements can be met. Moreover, we discuss slow long-term drift of the detector pointing due to orbital precession, and put forward stable orbits with six other pointings along the lunar orbital plane. Some implications of the findings are pointed out. |
gr-qc/9302011 | null | Lee Smolin | Finite, diffeomorphism invariant observables in quantum gravity | Latex, no figures, 30 pages, SU-GP-93/1-1 | Phys.Rev. D49 (1994) 4028-4040 | 10.1103/PhysRevD.49.4028 | null | gr-qc hep-th | null | Two sets of spatially diffeomorphism invariant operators are constructed in
the loop representation formulation of quantum gravity. This is done by
coupling general relativity to an anti- symmetric tensor gauge field and using
that field to pick out sets of surfaces, with boundaries, in the spatial three
manifold. The two sets of observables then measure the areas of these surfaces
and the Wilson loops for the self-dual connection around their boundaries. The
operators that represent these observables are finite and background
independent when constructed through a proper regularization procedure.
Furthermore, the spectra of the area operators are discrete so that the
possible values that one can obtain by a measurement of the area of a physical
surface in quantum gravity are valued in a discrete set that includes integral
multiples of half the Planck area. These results make possible the construction
of a correspondence between any three geometry whose curvature is small in
Planck units and a diffeomorphism invariant state of the gravitational and
matter fields. This correspondence relies on the approximation of the classical
geometry by a piecewise flat Regge manifold, which is then put in
correspondence with a diffeomorphism invariant state of the gravity-matter
system in which the matter fields specify the faces of the triangulation and
the gravitational field is in an eigenstate of the operators that measure their
areas.
| [
{
"created": "Wed, 10 Feb 1993 12:33:00 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Smolin",
"Lee",
""
]
] | Two sets of spatially diffeomorphism invariant operators are constructed in the loop representation formulation of quantum gravity. This is done by coupling general relativity to an anti- symmetric tensor gauge field and using that field to pick out sets of surfaces, with boundaries, in the spatial three manifold. The two sets of observables then measure the areas of these surfaces and the Wilson loops for the self-dual connection around their boundaries. The operators that represent these observables are finite and background independent when constructed through a proper regularization procedure. Furthermore, the spectra of the area operators are discrete so that the possible values that one can obtain by a measurement of the area of a physical surface in quantum gravity are valued in a discrete set that includes integral multiples of half the Planck area. These results make possible the construction of a correspondence between any three geometry whose curvature is small in Planck units and a diffeomorphism invariant state of the gravitational and matter fields. This correspondence relies on the approximation of the classical geometry by a piecewise flat Regge manifold, which is then put in correspondence with a diffeomorphism invariant state of the gravity-matter system in which the matter fields specify the faces of the triangulation and the gravitational field is in an eigenstate of the operators that measure their areas. |
gr-qc/0211056 | Kunimasa Yamada | Hisao Suzuki and Kunimasa Yamada | Analytic Evaluation of the Decay Rate for Accelerated Proton | 11 pages | Phys.Rev. D67 (2003) 065002 | 10.1103/PhysRevD.67.065002 | EPHOU 02-007 | gr-qc | null | We evaluate the decay rate of the uniformly accelerated proton. We obtain an
analytic expression for inverse beta decay process caused by the acceleration.
We evaluate the decay rate both from the inertial frame and from the
accelerated frame where we should consider thermal radiation by Unruh effect.
We explicitly check that the decay rates obtained in both frame coincide with
each other.
| [
{
"created": "Fri, 15 Nov 2002 05:54:02 GMT",
"version": "v1"
},
{
"created": "Tue, 10 Dec 2002 08:12:04 GMT",
"version": "v2"
},
{
"created": "Tue, 24 Dec 2002 08:34:10 GMT",
"version": "v3"
}
] | 2009-11-07 | [
[
"Suzuki",
"Hisao",
""
],
[
"Yamada",
"Kunimasa",
""
]
] | We evaluate the decay rate of the uniformly accelerated proton. We obtain an analytic expression for inverse beta decay process caused by the acceleration. We evaluate the decay rate both from the inertial frame and from the accelerated frame where we should consider thermal radiation by Unruh effect. We explicitly check that the decay rates obtained in both frame coincide with each other. |
gr-qc/0503092 | Marco Alberici | Marco Alberici | Measures and metrics in uniform gravitational fields | revtex4, 13 pages, 6 figures. Description was symplified and few
formula were corrected. One bibliografy link was also corrected and footnote
5 (4 in the previous version) was completely rewritten | null | null | null | gr-qc physics.ed-ph | null | A partially alternative derivation of the expression for the time dilation
effect in a uniform static gravitational field is obtained by means of a
thought experiment in which rates of clocks at rest at different heights are
compared using as reference a clock bound to a free falling reference system
(FFRS). Derivations along these lines have already been proposed, but generally
introducing some shortcut in order to make the presentation elementary. The
treatment is here exact: the clocks whose rates one wishes to compare are let
to describe their world lines (Rindler's hyperbolae) with respect to the FFRS,
and the result is obtained by comparing their lengths in space-time. The
exercise may nonetheless prove pedagogically instructive insofar as it shows
that the some results of General Relativity (GR) can be obtained in terms of
physical and geometrical reasoning without having recourse to the general
formalism. The corresponding GR metric is derived, to the purpose of making a
comparison with solutions of Einstein field equation and with other metrics.
For this reasons this paper also compels to deal with a few subtle points
inherent in the very foundations of GR.
| [
{
"created": "Mon, 21 Mar 2005 18:36:18 GMT",
"version": "v1"
},
{
"created": "Thu, 12 May 2005 16:10:32 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Alberici",
"Marco",
""
]
] | A partially alternative derivation of the expression for the time dilation effect in a uniform static gravitational field is obtained by means of a thought experiment in which rates of clocks at rest at different heights are compared using as reference a clock bound to a free falling reference system (FFRS). Derivations along these lines have already been proposed, but generally introducing some shortcut in order to make the presentation elementary. The treatment is here exact: the clocks whose rates one wishes to compare are let to describe their world lines (Rindler's hyperbolae) with respect to the FFRS, and the result is obtained by comparing their lengths in space-time. The exercise may nonetheless prove pedagogically instructive insofar as it shows that the some results of General Relativity (GR) can be obtained in terms of physical and geometrical reasoning without having recourse to the general formalism. The corresponding GR metric is derived, to the purpose of making a comparison with solutions of Einstein field equation and with other metrics. For this reasons this paper also compels to deal with a few subtle points inherent in the very foundations of GR. |
1302.6860 | Alexander Kamenshchik | A. Kamenshchik and S. Manti | Classical and quantum Big Brake cosmology for scalar field and tachyonic
models | 8 pages, published in the Proceedings of the International conference
"Multiverse and Fundamental Cosmology: Multicosmofun '12", September 10-14,
Szczein, Poland edited by Mariusz P. Dabrowski, Adam Balcerzak, Tomasz
Denkiewicz | AIP Conf. Proc. 1514, 179-182 (2013) | 10.1063/1.4791751 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study a relation between the cosmological singularities in classical and
quantum theory, comparing the classical and quantum dynamics in some models
possessing the Big Brake singularity - the model based on a scalar field and
two models based on a tachyon-pseudo-tachyon field . It is shown that the
effect of quantum avoidance is absent for the soft singularities of the Big
Brake type while it is present for the Big Bang and Big Crunch singularities.
Thus, there is some kind of a classical - quantum correspondence, because soft
singularities are traversable in classical cosmology, while the strong Big Bang
and Big Crunch singularities are not traversable.
| [
{
"created": "Wed, 27 Feb 2013 14:39:39 GMT",
"version": "v1"
}
] | 2015-06-15 | [
[
"Kamenshchik",
"A.",
""
],
[
"Manti",
"S.",
""
]
] | We study a relation between the cosmological singularities in classical and quantum theory, comparing the classical and quantum dynamics in some models possessing the Big Brake singularity - the model based on a scalar field and two models based on a tachyon-pseudo-tachyon field . It is shown that the effect of quantum avoidance is absent for the soft singularities of the Big Brake type while it is present for the Big Bang and Big Crunch singularities. Thus, there is some kind of a classical - quantum correspondence, because soft singularities are traversable in classical cosmology, while the strong Big Bang and Big Crunch singularities are not traversable. |
1812.02110 | Muxin Han | Muxin Han, Zichang Huang, Antonia Zipfel | Emergent 4-dimensional linearized gravity from spin foam model | 15+5 pages, 4 figures. V2 improves the presentation, and expands the
discussion on the geometrical correspondence of spinfoam large-j critical
points | Phys. Rev. D 100, 024060 (2019) | 10.1103/PhysRevD.100.024060 | null | gr-qc cond-mat.str-el hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Spin Foam Models (SFMs) are covariant formulations of Loop Quantum Gravity
(LQG) in 4 dimensions. This work studies the perturbations of SFMs on a flat
background. It demonstrates for the first time that smooth curved spacetime
geometries satisfying Einstein equation can emerge from discrete SFMs under an
appropriate low energy limit, which corresponds to a semiclassical continuum
limit of SFMs. In particular, we show that the low energy excitations of SFMs
on a flat background give all smooth solutions of linearized Einstein equations
(spin-2 gravitons). This indicates that at the linearized level, classical
Einstein gravity is indeed the low energy effective theory from SFMs. Thus our
result heightens the confidence that covariant LQG is a consistent theory of
quantum gravity. As a key technical tool, a regularization/deformation of the
SFM is employed in the derivation. The deformation parameter $\delta$ becomes a
coupling constant of a higher curvature correction term to Einstein gravity
from SFM.
| [
{
"created": "Wed, 5 Dec 2018 17:00:09 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Apr 2019 17:50:30 GMT",
"version": "v2"
}
] | 2019-08-07 | [
[
"Han",
"Muxin",
""
],
[
"Huang",
"Zichang",
""
],
[
"Zipfel",
"Antonia",
""
]
] | Spin Foam Models (SFMs) are covariant formulations of Loop Quantum Gravity (LQG) in 4 dimensions. This work studies the perturbations of SFMs on a flat background. It demonstrates for the first time that smooth curved spacetime geometries satisfying Einstein equation can emerge from discrete SFMs under an appropriate low energy limit, which corresponds to a semiclassical continuum limit of SFMs. In particular, we show that the low energy excitations of SFMs on a flat background give all smooth solutions of linearized Einstein equations (spin-2 gravitons). This indicates that at the linearized level, classical Einstein gravity is indeed the low energy effective theory from SFMs. Thus our result heightens the confidence that covariant LQG is a consistent theory of quantum gravity. As a key technical tool, a regularization/deformation of the SFM is employed in the derivation. The deformation parameter $\delta$ becomes a coupling constant of a higher curvature correction term to Einstein gravity from SFM. |
2306.08246 | Seema Satin | Seema Satin | Induced polar perturbations in relativistic stars with stochastic
effects in the dense matter at sub-hydro mesoscopic scales: A theoretical
probe at intermediate length scales | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A linear response relation between metric and fluid perturbations driven by a
background noise source is used as a framework for obtaining non-radial polar
perturbations in dense matter relativistic stars. The perturbations carry a
generalized stochastic nature as solutions to the classical Einstein-Langevin
equation which has been recently proposed. The significance of these stochastic
non-radial polar perturbations lies at probing the intermediate sub-hydro
scales inside the dense fluid. This study extends towards a
non-equilibrium/near-equilibrium statistical mechanics study for relativistic
star interiors. We address the non-radial polar perturbations in stars which
are important from the point of view of detection in future. A generalized
stochastic noise which originates as the remnant of collapse mechanism in
isolated star is expected to give rise to such stochastic polar perturbations
at intermediate sub-hydro scales. More specifically it is the interplay between
the degeneracy pressure of exotic matter and the gravitational pressure that
gives rise to the seeds of stochastic effects or noise in the background of the
gravitating body towards the near-equilibrium configuration.
| [
{
"created": "Wed, 14 Jun 2023 05:18:48 GMT",
"version": "v1"
}
] | 2023-06-16 | [
[
"Satin",
"Seema",
""
]
] | A linear response relation between metric and fluid perturbations driven by a background noise source is used as a framework for obtaining non-radial polar perturbations in dense matter relativistic stars. The perturbations carry a generalized stochastic nature as solutions to the classical Einstein-Langevin equation which has been recently proposed. The significance of these stochastic non-radial polar perturbations lies at probing the intermediate sub-hydro scales inside the dense fluid. This study extends towards a non-equilibrium/near-equilibrium statistical mechanics study for relativistic star interiors. We address the non-radial polar perturbations in stars which are important from the point of view of detection in future. A generalized stochastic noise which originates as the remnant of collapse mechanism in isolated star is expected to give rise to such stochastic polar perturbations at intermediate sub-hydro scales. More specifically it is the interplay between the degeneracy pressure of exotic matter and the gravitational pressure that gives rise to the seeds of stochastic effects or noise in the background of the gravitating body towards the near-equilibrium configuration. |
gr-qc/0109097 | Andre Fuzfa | A. Fuzfa, J.M. Gerard, D. Lambert | The Lemaitre-Schwarzschild Problem Revisited | Final version as accepted by GR&G (to appear in vol. 34, september
2002) | Gen.Rel.Grav. 34 (2002) 1411-1422 | 10.1023/A:1020030919033 | null | gr-qc | null | The Lemaitre and Schwarzschild analytical solutions for a relativistic
spherical body of constant density are linked together through the use of the
Weyl quadratic invariant. The critical radius for gravitational collapse of an
incompressible fluid is shown to vary continuously from 9/8 of the
Schwarzschild radius to the Schwarzschild radius itself while the internal
pressures become locally anisotropic.
| [
{
"created": "Fri, 28 Sep 2001 17:24:59 GMT",
"version": "v1"
},
{
"created": "Fri, 26 Oct 2001 13:55:48 GMT",
"version": "v2"
},
{
"created": "Thu, 14 Mar 2002 10:10:56 GMT",
"version": "v3"
}
] | 2015-06-25 | [
[
"Fuzfa",
"A.",
""
],
[
"Gerard",
"J. M.",
""
],
[
"Lambert",
"D.",
""
]
] | The Lemaitre and Schwarzschild analytical solutions for a relativistic spherical body of constant density are linked together through the use of the Weyl quadratic invariant. The critical radius for gravitational collapse of an incompressible fluid is shown to vary continuously from 9/8 of the Schwarzschild radius to the Schwarzschild radius itself while the internal pressures become locally anisotropic. |
1801.08359 | Patryk Mach | Patryk Mach and Jerzy Knopik | Rotating Bowen-York initial data with a positive cosmological constant | 24 pages, 9 figures | null | 10.1088/1361-6382/aac585 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A generalization of the Bowen-York initial data to the case with a positive
cosmological constant is investigated. We follow the construction presented
recently by Bizo\'n, Pletka and Simon, and solve numerically the Lichnerowicz
equation on a compactified domain $\mathbb S^1 \times \mathbb S^2$. In addition
to two branches of solutions depending on the polar variable on $\mathbb S^2$
that were already known, we find branches of solutions depending on two
variables: the polar variable on $\mathbb S^2$ and the coordinate on $\mathbb
S^1$. Using Vanderbauwhede's results concerning bifurcations from symmetric
solutions, we show the existence of the corresponding bifurcation points. By
linearizing the Lichnerowicz equation and solving the resulting eigenvalue
problem, we collect numerical evidence suggesting the absence of additional
branches of solutions.
| [
{
"created": "Thu, 25 Jan 2018 11:25:25 GMT",
"version": "v1"
}
] | 2018-07-11 | [
[
"Mach",
"Patryk",
""
],
[
"Knopik",
"Jerzy",
""
]
] | A generalization of the Bowen-York initial data to the case with a positive cosmological constant is investigated. We follow the construction presented recently by Bizo\'n, Pletka and Simon, and solve numerically the Lichnerowicz equation on a compactified domain $\mathbb S^1 \times \mathbb S^2$. In addition to two branches of solutions depending on the polar variable on $\mathbb S^2$ that were already known, we find branches of solutions depending on two variables: the polar variable on $\mathbb S^2$ and the coordinate on $\mathbb S^1$. Using Vanderbauwhede's results concerning bifurcations from symmetric solutions, we show the existence of the corresponding bifurcation points. By linearizing the Lichnerowicz equation and solving the resulting eigenvalue problem, we collect numerical evidence suggesting the absence of additional branches of solutions. |
gr-qc/9508019 | Andrei Linde | Andrei Linde | Quantum Cosmology and the Structure of Inflationary Universe | 43 pages, LaTeX, Invited talk at the joint Johns Hopkins Workshop -
PASCOS meeting, Baltimore, 1995 | null | null | SU-ITP-95-15 | gr-qc astro-ph hep-ph hep-th | null | In this review I consider several different issues related to inflation. I
will begin with the wave function of the Universe. This issue is pretty old,
but recently there were some new insights based on the theory of the
self-reproducing inflationary universe. Then we will discuss stationarity of
inflationary universe and the possibility to make predictions in the context of
quantum cosmology using stochastic approach to inflation. Returning to more
pragmatic aspects of inflationary theory, we will discuss inflationary models
with $\Omega < 1$. Finally, we will describe several aspects of the theory of
reheating of the Universe based on the effect of parametric resonance.
| [
{
"created": "Tue, 8 Aug 1995 02:08:11 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Linde",
"Andrei",
""
]
] | In this review I consider several different issues related to inflation. I will begin with the wave function of the Universe. This issue is pretty old, but recently there were some new insights based on the theory of the self-reproducing inflationary universe. Then we will discuss stationarity of inflationary universe and the possibility to make predictions in the context of quantum cosmology using stochastic approach to inflation. Returning to more pragmatic aspects of inflationary theory, we will discuss inflationary models with $\Omega < 1$. Finally, we will describe several aspects of the theory of reheating of the Universe based on the effect of parametric resonance. |
gr-qc/0002091 | Valerio Faraoni | Valerio Faraoni (Universite' Libre de Bruxelles) | Inflation and quintessence with nonminimal coupling | 36 pages, LaTeX. Typos in Eq. (2.5) corrected | Phys.Rev.D62:023504,2000 | 10.1103/PhysRevD.62.023504 | null | gr-qc astro-ph hep-th | null | The nonminimal coupling (NMC) of the scalar field to the Ricci curvature is
unavoidable in many cosmological scenarios. Inflation and quintessence models
based on nonminimally coupled scalar fields are studied, with particular
attention to the balance between the scalar potential and the NMC term in the
action. NMC makes acceleration of the universe harder to achieve for the usual
potentials, but it is beneficial in obtaining cosmic acceleration with unusual
potentials. The slow-roll approximation with NMC, conformal transformation
techniques, and other aspects of the physics of NMC are clarified.
| [
{
"created": "Sat, 26 Feb 2000 15:00:58 GMT",
"version": "v1"
},
{
"created": "Mon, 17 Apr 2000 08:16:10 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Faraoni",
"Valerio",
"",
"Universite' Libre de Bruxelles"
]
] | The nonminimal coupling (NMC) of the scalar field to the Ricci curvature is unavoidable in many cosmological scenarios. Inflation and quintessence models based on nonminimally coupled scalar fields are studied, with particular attention to the balance between the scalar potential and the NMC term in the action. NMC makes acceleration of the universe harder to achieve for the usual potentials, but it is beneficial in obtaining cosmic acceleration with unusual potentials. The slow-roll approximation with NMC, conformal transformation techniques, and other aspects of the physics of NMC are clarified. |
2312.07017 | Jing Tan | Jing Tan and Baoxiang Wang | Constraints on Brans-Dicke gravity from neutron star-black hole merger
events using higher harmonics | 8 pages, 2 figures, 2 tables | Phys.Rev.D 109 (2024) 8, 084036 | 10.1103/PhysRevD.109.084036 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we derive a 90\% credible lower bound on the modified
parameter of scalar-tensor theories as $\varphi_{-2}>-7.94\times10^{-4}$ by
using dominant-mode correction. Specific to BD theory, we have the constraint
$\omega_{\rm BD}>4.75$. Asymmetric binary systems usually have a significant
mass ratio; in such cases, higher harmonic modes cannot be neglected. Our work
considers higher harmonic corrections from scalar-tensor theories and provides
a tighter constraint of $\varphi_{-2}>-7.59\times10^{-4}$. Transitioning to the
BD theory, the constraint is $\omega_{\rm BD}>5.06$, with a 6.5\% improvement.
We also consider a plausible NSBH event, GW190814, which is a highly unequal
mass ratio source and exhibits strong evidence for higher-order multipoles. We
obtain poorly converged results when using the dominant mode while getting a
constraint of $\varphi_{-2}>-6.60\times10^{-4}$ on scalar-tensor theories when
including the higher harmonic modes. This suggests that the difference between
the dominant mode and higher modes has a significant impact on our analysis.
Furthermore, treating this suspected event as an NSBH event, we find
$\omega_{\rm BD}>6.12$ when including the higher harmonic modes. Combining
GW200115 and GW190814 and including higher modes, the constraint is improved to
$\omega_{\rm BD}>110.55$. This is currently the strongest constraint utilizing
GWs, contingent upon GW190814 being an NSBH event. Additionally, we take into
account a BD-like theory, known as screened modified gravity (SMG), and
investigate the coupling constant constraints, both with and without
higher-mode corrections, by using data from both GW200115 and GW190814.
| [
{
"created": "Tue, 12 Dec 2023 07:08:53 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Apr 2024 14:22:21 GMT",
"version": "v2"
},
{
"created": "Sun, 28 Apr 2024 17:45:25 GMT",
"version": "v3"
}
] | 2024-04-30 | [
[
"Tan",
"Jing",
""
],
[
"Wang",
"Baoxiang",
""
]
] | In this paper, we derive a 90\% credible lower bound on the modified parameter of scalar-tensor theories as $\varphi_{-2}>-7.94\times10^{-4}$ by using dominant-mode correction. Specific to BD theory, we have the constraint $\omega_{\rm BD}>4.75$. Asymmetric binary systems usually have a significant mass ratio; in such cases, higher harmonic modes cannot be neglected. Our work considers higher harmonic corrections from scalar-tensor theories and provides a tighter constraint of $\varphi_{-2}>-7.59\times10^{-4}$. Transitioning to the BD theory, the constraint is $\omega_{\rm BD}>5.06$, with a 6.5\% improvement. We also consider a plausible NSBH event, GW190814, which is a highly unequal mass ratio source and exhibits strong evidence for higher-order multipoles. We obtain poorly converged results when using the dominant mode while getting a constraint of $\varphi_{-2}>-6.60\times10^{-4}$ on scalar-tensor theories when including the higher harmonic modes. This suggests that the difference between the dominant mode and higher modes has a significant impact on our analysis. Furthermore, treating this suspected event as an NSBH event, we find $\omega_{\rm BD}>6.12$ when including the higher harmonic modes. Combining GW200115 and GW190814 and including higher modes, the constraint is improved to $\omega_{\rm BD}>110.55$. This is currently the strongest constraint utilizing GWs, contingent upon GW190814 being an NSBH event. Additionally, we take into account a BD-like theory, known as screened modified gravity (SMG), and investigate the coupling constant constraints, both with and without higher-mode corrections, by using data from both GW200115 and GW190814. |
0911.2064 | Antoine Folacci | Antoine Folacci | BRST quantization of the massless minimally coupled scalar field in de
Sitter space (zero modes, euclideanization and quantization) | This paper has been published under the title "Zero modes,
euclideanization and quantization" [Phys. Rev. D46, 2553 (1992)] | Phys.Rev.D46:2553-2559,1992 | 10.1103/PhysRevD.46.2553 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the massless scalar field on the four-dimensional sphere $S^4$.
Its classical action $S={1\over 2}\int_{S^4} dV (\nabla \phi)^2$ is degenerate
under the global invariance $\phi \to \phi + \hbox{constant}$. We then quantize
the massless scalar field as a gauge theory by constructing a BRST-invariant
quantum action. The corresponding gauge-breaking term is a non-local one of the
form $S^{\rm GB}={1\over {2\alpha V}}\bigl(\int_{S^4} dV \phi \bigr)^2$ where
$\alpha$ is a gauge parameter and $V$ is the volume of $S^4$. It allows us to
correctly treat the zero mode problem. The quantum theory is invariant under
SO(5), the symmetry group of $S^4$, and the associated two-point functions have
no infrared divergence. The well-known infrared divergence which appears by
taking the massless limit of the massive scalar field propagator is therefore a
gauge artifact. By contrast, the massless scalar field theory on de Sitter
space $dS^4$ - the lorentzian version of $S^4$ - is not invariant under the
symmetry group of that spacetime SO(1,4). Here, the infrared divergence is
real. Therefore, the massless scalar quantum field theories on $S^4$ and $dS^4$
cannot be linked by analytic continuation. In this case, because of zero modes,
the euclidean approach to quantum field theory does not work. Similar
considerations also apply to massive scalar field theories for exceptional
values of the mass parameter (corresponding to the discrete series of the de
Sitter group).
| [
{
"created": "Wed, 11 Nov 2009 16:27:42 GMT",
"version": "v1"
}
] | 2010-04-21 | [
[
"Folacci",
"Antoine",
""
]
] | We consider the massless scalar field on the four-dimensional sphere $S^4$. Its classical action $S={1\over 2}\int_{S^4} dV (\nabla \phi)^2$ is degenerate under the global invariance $\phi \to \phi + \hbox{constant}$. We then quantize the massless scalar field as a gauge theory by constructing a BRST-invariant quantum action. The corresponding gauge-breaking term is a non-local one of the form $S^{\rm GB}={1\over {2\alpha V}}\bigl(\int_{S^4} dV \phi \bigr)^2$ where $\alpha$ is a gauge parameter and $V$ is the volume of $S^4$. It allows us to correctly treat the zero mode problem. The quantum theory is invariant under SO(5), the symmetry group of $S^4$, and the associated two-point functions have no infrared divergence. The well-known infrared divergence which appears by taking the massless limit of the massive scalar field propagator is therefore a gauge artifact. By contrast, the massless scalar field theory on de Sitter space $dS^4$ - the lorentzian version of $S^4$ - is not invariant under the symmetry group of that spacetime SO(1,4). Here, the infrared divergence is real. Therefore, the massless scalar quantum field theories on $S^4$ and $dS^4$ cannot be linked by analytic continuation. In this case, because of zero modes, the euclidean approach to quantum field theory does not work. Similar considerations also apply to massive scalar field theories for exceptional values of the mass parameter (corresponding to the discrete series of the de Sitter group). |
1603.01117 | Etera R. Livine | Christoph Charles and Etera R. Livine | The Fock Space of Loopy Spin Networks for Quantum Gravity | 53 pages, all figures in tikz (v2: typo corrected in eqn 135-136) | General Relativity and Gravitation, August 2016, 48:113 | 10.1007/s10714-016-2107-5 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the context of the coarse-graining of loop quantum gravity, we introduce
loopy and tagged spin networks, which generalize the standard spin network
states to account explicitly for non-trivial curvature and torsion. Both
structures relax the closure constraints imposed at the spin network vertices.
While tagged spin networks merely carry an extra spin at every vertex encoding
the overall closure defect, loopy spin networks allow for an arbitrary number
of loops attached to each vertex. These little loops can be interpreted as
local excitations of the quantum gravitational field and we discuss the
statistics to endow them with. The resulting Fock space of loopy spin networks
realizes new truncation of loop quantum gravity, allowing to formulate its
graph-changing dynamics on a fixed background graph plus local degrees of
freedom attached to the graph nodes. This provides a framework for
re-introducing a non-trivial background quantum geometry around which we would
study the effective dynamics of perturbations. We study how to implement the
dynamics of topological BF theory in this framework. We realize the projection
on flat connections through holonomy constraints and we pay special attention
to their often overlooked non-trivial flat solutions defined by higher
derivatives of the $\delta$-distribution.
| [
{
"created": "Thu, 3 Mar 2016 14:59:18 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Mar 2016 12:48:34 GMT",
"version": "v2"
}
] | 2016-08-11 | [
[
"Charles",
"Christoph",
""
],
[
"Livine",
"Etera R.",
""
]
] | In the context of the coarse-graining of loop quantum gravity, we introduce loopy and tagged spin networks, which generalize the standard spin network states to account explicitly for non-trivial curvature and torsion. Both structures relax the closure constraints imposed at the spin network vertices. While tagged spin networks merely carry an extra spin at every vertex encoding the overall closure defect, loopy spin networks allow for an arbitrary number of loops attached to each vertex. These little loops can be interpreted as local excitations of the quantum gravitational field and we discuss the statistics to endow them with. The resulting Fock space of loopy spin networks realizes new truncation of loop quantum gravity, allowing to formulate its graph-changing dynamics on a fixed background graph plus local degrees of freedom attached to the graph nodes. This provides a framework for re-introducing a non-trivial background quantum geometry around which we would study the effective dynamics of perturbations. We study how to implement the dynamics of topological BF theory in this framework. We realize the projection on flat connections through holonomy constraints and we pay special attention to their often overlooked non-trivial flat solutions defined by higher derivatives of the $\delta$-distribution. |
gr-qc/0503034 | Vicente Jos\'e Bol\'os | V. J. Bolos, V. Liern, J. Olivert | Relativistic simultaneity and causality | 12 pages, 5 figures. This is a totally revised version of the paper
of same title | Int.J.Theor.Phys. 41:1007-1018,2002 | 10.1023/A:1016079025682 | null | gr-qc | null | We analyze two types of relativistic simultaneity associated to an observer:
the spacelike simultaneity, given by Landau submanifolds, and the lightlike
simultaneity (also known as observed simultaneity), given by past-pointing
horismos submanifolds. We study some geometrical conditions to ensure that
Landau submanifolds are spacelike and we prove that horismos submanifolds are
always lightlike. Finally, we establish some conditions to guarantee the
existence of foliations in the space-time whose leaves are these submanifolds
of simultaneity generated by an observer.
| [
{
"created": "Wed, 9 Mar 2005 15:13:52 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Bolos",
"V. J.",
""
],
[
"Liern",
"V.",
""
],
[
"Olivert",
"J.",
""
]
] | We analyze two types of relativistic simultaneity associated to an observer: the spacelike simultaneity, given by Landau submanifolds, and the lightlike simultaneity (also known as observed simultaneity), given by past-pointing horismos submanifolds. We study some geometrical conditions to ensure that Landau submanifolds are spacelike and we prove that horismos submanifolds are always lightlike. Finally, we establish some conditions to guarantee the existence of foliations in the space-time whose leaves are these submanifolds of simultaneity generated by an observer. |
1612.01299 | Salvatore Capozziello | Sebastian Bahamonde, and Salvatore Capozziello | Noether Symmetry Approach in $f(T,B)$ teleparallel cosmology | 21 pages | null | 10.1140/epjc/s10052-017-4677-0 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the cosmology derived from $f(T,B)$ gravity where $T$ is the
torsion scalar and $B=\frac{2}{e}\partial_{\mu}(e T^{\mu})$ a boundary term. In
particular we discuss how it is possible to recover, under the same standard,
the teleparallel $f(T)$ gravity, the curvature $f(R)$ gravity and the
teleparallel-curvature $f(R,T)$ gravity, which are particular cases of
$f(T,B)$. We adopt the Noether Symmetry Approach to study the related dynamical
systems and to find out cosmological solutions.
| [
{
"created": "Mon, 5 Dec 2016 10:29:43 GMT",
"version": "v1"
}
] | 2017-03-08 | [
[
"Bahamonde",
"Sebastian",
""
],
[
"Capozziello",
"Salvatore",
""
]
] | We consider the cosmology derived from $f(T,B)$ gravity where $T$ is the torsion scalar and $B=\frac{2}{e}\partial_{\mu}(e T^{\mu})$ a boundary term. In particular we discuss how it is possible to recover, under the same standard, the teleparallel $f(T)$ gravity, the curvature $f(R)$ gravity and the teleparallel-curvature $f(R,T)$ gravity, which are particular cases of $f(T,B)$. We adopt the Noether Symmetry Approach to study the related dynamical systems and to find out cosmological solutions. |
1109.5858 | Burkhard Kleihaus | Burkhard Kleihaus, Jutta Kunz and Stefanie Schneider | Stable Phases of Boson Stars | 18 pages, 14 figures | null | 10.1103/PhysRevD.85.024045 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the physical properties of boson stars, which possess counterparts
in flat space-time, Q-balls. Applying a stability analysis via catastrophe
theory, we show that the families of rotating and non-rotating boson stars
exhibit two stable regions, separated by an unstable region. Analogous to the
case of white dwarfs and neutron stars, these two regions correspond to compact
stars of lower and higher density. Moreover, the high density phase ends when
the black hole limit is approached. Here another unstable phase is encountered,
exhibiting the typical spiralling phenomenon close to the black hole limit.
When the interaction terms in the scalar field potential become negligible, the
properties of mini boson stars are recovered, which possess only a single
stable phase.
| [
{
"created": "Tue, 27 Sep 2011 12:28:23 GMT",
"version": "v1"
}
] | 2013-05-30 | [
[
"Kleihaus",
"Burkhard",
""
],
[
"Kunz",
"Jutta",
""
],
[
"Schneider",
"Stefanie",
""
]
] | We analyze the physical properties of boson stars, which possess counterparts in flat space-time, Q-balls. Applying a stability analysis via catastrophe theory, we show that the families of rotating and non-rotating boson stars exhibit two stable regions, separated by an unstable region. Analogous to the case of white dwarfs and neutron stars, these two regions correspond to compact stars of lower and higher density. Moreover, the high density phase ends when the black hole limit is approached. Here another unstable phase is encountered, exhibiting the typical spiralling phenomenon close to the black hole limit. When the interaction terms in the scalar field potential become negligible, the properties of mini boson stars are recovered, which possess only a single stable phase. |
2201.06558 | David Brown | J. David Brown | Singular Lagrangians, Constrained Hamiltonian Systems and Gauge
Invariance: An Example of the Dirac-Bergmann Algorithm | Final Version | Universe 2022, 8(3), 171 | 10.3390/universe8030171 | null | gr-qc hep-th math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | The Dirac-Bergmann algorithm is a recipe for converting a theory with a
singular Lagrangian into a constrained Hamiltonian system. Constrained
Hamiltonian systems include gauge theories -- general relativity,
electromagnetism, Yang Mills, string theory, etc. The Dirac-Bergmann algorithm
is elegant but at the same time rather complicated. It consists of a large
number of logical steps linked together by a subtle chain of reasoning.
Examples of the Dirac-Bergmann algorithm found in the literature are designed
to isolate and illustrate just one or two of those logical steps. In this paper
I analyze a finite-dimensional system that exhibits all of the major steps in
the algorithm. The system includes primary and secondary constraints, first and
second class constraints, restrictions on Lagrange multipliers, and both
physical and gauge degrees of freedom. This relatively simple system provides a
platform for discussing the Dirac conjecture, constructing Dirac brackets, and
applying gauge conditions.
| [
{
"created": "Mon, 17 Jan 2022 18:25:38 GMT",
"version": "v1"
},
{
"created": "Fri, 21 Jan 2022 23:20:33 GMT",
"version": "v2"
},
{
"created": "Wed, 9 Mar 2022 14:27:44 GMT",
"version": "v3"
}
] | 2022-03-10 | [
[
"Brown",
"J. David",
""
]
] | The Dirac-Bergmann algorithm is a recipe for converting a theory with a singular Lagrangian into a constrained Hamiltonian system. Constrained Hamiltonian systems include gauge theories -- general relativity, electromagnetism, Yang Mills, string theory, etc. The Dirac-Bergmann algorithm is elegant but at the same time rather complicated. It consists of a large number of logical steps linked together by a subtle chain of reasoning. Examples of the Dirac-Bergmann algorithm found in the literature are designed to isolate and illustrate just one or two of those logical steps. In this paper I analyze a finite-dimensional system that exhibits all of the major steps in the algorithm. The system includes primary and secondary constraints, first and second class constraints, restrictions on Lagrange multipliers, and both physical and gauge degrees of freedom. This relatively simple system provides a platform for discussing the Dirac conjecture, constructing Dirac brackets, and applying gauge conditions. |
2403.08400 | Alexander Kamenshchik | Alexander Kamenshchik and Polina Petriakova | Regular Friedmann Universes and Matter Transformations | 11 pages, 2 figures | Published in Universe, 10 (3) 137 (2024), Special Issue "The
Friedmann Cosmology: A Century Later" | 10.3390/universe10030137 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We apply a very simple procedure to construct non-singular cosmological
models for flat Friedmann universes filled with minimally coupled scalar fields
or by tachyon Born-Infeld-type fields. Remarkably, for the minimally coupled
scalar field and the tachyon field, the regularity of the cosmological
evolution, or in other words, the existence of bounce, implies the necessity of
the transition between scalar fields with standard kinetic terms to those with
phantom ones. In both cases, the potentials in the vicinity of the point of the
transition have a non-analyticity of the cusp form that is characterized by the
same exponent and is equal to 2/3. If, in the tachyon models evolution, the
pressure changes its sign, then another transformation of the Born-Infeld-type
field occurs: the tachyon transforms into a pseudotachyon, and vice versa. We
also undertake an analysis of the stability of the cosmological evolution in
our models; we rely on the study of the speed of sound squared.
| [
{
"created": "Wed, 13 Mar 2024 10:28:48 GMT",
"version": "v1"
}
] | 2024-03-14 | [
[
"Kamenshchik",
"Alexander",
""
],
[
"Petriakova",
"Polina",
""
]
] | We apply a very simple procedure to construct non-singular cosmological models for flat Friedmann universes filled with minimally coupled scalar fields or by tachyon Born-Infeld-type fields. Remarkably, for the minimally coupled scalar field and the tachyon field, the regularity of the cosmological evolution, or in other words, the existence of bounce, implies the necessity of the transition between scalar fields with standard kinetic terms to those with phantom ones. In both cases, the potentials in the vicinity of the point of the transition have a non-analyticity of the cusp form that is characterized by the same exponent and is equal to 2/3. If, in the tachyon models evolution, the pressure changes its sign, then another transformation of the Born-Infeld-type field occurs: the tachyon transforms into a pseudotachyon, and vice versa. We also undertake an analysis of the stability of the cosmological evolution in our models; we rely on the study of the speed of sound squared. |
0902.0307 | Stephen Fairhurst | Benjamin Farr, Stephen Fairhurst, B.S. Sathyaprakash | Searching for binary coalescences with inspiral templates: Detection and
parameter estimation | 14 pages, submitted to proceedings of the NRDA08 meeting, Syracuse,
Aug. 11-14, 2008 | Class.Quant.Grav.26:114009,2009 | 10.1088/0264-9381/26/11/114009 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There has been remarkable progress in numerical relativity recently. This has
led to the generation of gravitational waveform signals covering what has been
traditionally termed the three phases of the coalescence of a compact binary -
the inspiral, merger and ringdown. In this paper, we examine the usefulness of
inspiral only templates for both detection and parameter estimation of the full
coalescence waveforms generated by numerical relativity simulations. To this
end, we deploy as search templates waveforms based on the effective one-body
waveforms terminated at the light-ring as well as standard post-Newtonian
waveforms. We find that both of these are good for detection of signals.
Parameter estimation is good at low masses, but degrades as the mass of the
binary system increases.
| [
{
"created": "Mon, 2 Feb 2009 15:50:50 GMT",
"version": "v1"
}
] | 2009-06-10 | [
[
"Farr",
"Benjamin",
""
],
[
"Fairhurst",
"Stephen",
""
],
[
"Sathyaprakash",
"B. S.",
""
]
] | There has been remarkable progress in numerical relativity recently. This has led to the generation of gravitational waveform signals covering what has been traditionally termed the three phases of the coalescence of a compact binary - the inspiral, merger and ringdown. In this paper, we examine the usefulness of inspiral only templates for both detection and parameter estimation of the full coalescence waveforms generated by numerical relativity simulations. To this end, we deploy as search templates waveforms based on the effective one-body waveforms terminated at the light-ring as well as standard post-Newtonian waveforms. We find that both of these are good for detection of signals. Parameter estimation is good at low masses, but degrades as the mass of the binary system increases. |
1909.08698 | Pedro Moraes | M.M. Lapola, P.H.R.S. Moraes, W. de Paula, J. F. Jesus, R. Valentim,
M. Malheiro | A unique equation of state for the universe evolution from AdS$_5$
space-time | 14 pages, 11 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We apply the Induced Matter Model to a five-dimensional metric. For the case
with null cosmological constant, we obtain a solution able to describe the
radiation-dominated era of the universe. The positive $\Lambda$ case yields a
bounce cosmological model. In the negative five-dimensional cosmological
constant case, the scale factor is obtained as $a(t)\sim\sqrt[]{\sinh t}$,
which is able to describe not only the late-time cosmic acceleration but also
the non-accelerated stages of the cosmic expansion in a continuous form. This
solution together with the extra-dimensional scale factor solution yields the
material content of the model to be remarkably related through an equation of
state analogous to the renowned MIT bag model equation of state for quark
matter $p=(\rho-4B)/3$. In our case, $\rho=\rho_m+B$, with $\rho_m$ being the
energy density of relativistic and non-relativistic matter and $B=\ \Lambda\
/16\pi$ represents the bag energy constant, which plays the role of the dark
energy in the four-dimensional universe, with $\Lambda$ being the cosmological
constant of the AdS$_5$ space-time. Our model satisfactorily fits the
observational data for the low redshift sample of the experimental measurement
of the Hubble parameter, which resulted in $H_0=72.2^{+5.3}_{-5.5}$km s$^{-1}$
Mpc$^{-1}$.
| [
{
"created": "Wed, 18 Sep 2019 20:47:17 GMT",
"version": "v1"
}
] | 2019-09-20 | [
[
"Lapola",
"M. M.",
""
],
[
"Moraes",
"P. H. R. S.",
""
],
[
"de Paula",
"W.",
""
],
[
"Jesus",
"J. F.",
""
],
[
"Valentim",
"R.",
""
],
[
"Malheiro",
"M.",
""
]
] | We apply the Induced Matter Model to a five-dimensional metric. For the case with null cosmological constant, we obtain a solution able to describe the radiation-dominated era of the universe. The positive $\Lambda$ case yields a bounce cosmological model. In the negative five-dimensional cosmological constant case, the scale factor is obtained as $a(t)\sim\sqrt[]{\sinh t}$, which is able to describe not only the late-time cosmic acceleration but also the non-accelerated stages of the cosmic expansion in a continuous form. This solution together with the extra-dimensional scale factor solution yields the material content of the model to be remarkably related through an equation of state analogous to the renowned MIT bag model equation of state for quark matter $p=(\rho-4B)/3$. In our case, $\rho=\rho_m+B$, with $\rho_m$ being the energy density of relativistic and non-relativistic matter and $B=\ \Lambda\ /16\pi$ represents the bag energy constant, which plays the role of the dark energy in the four-dimensional universe, with $\Lambda$ being the cosmological constant of the AdS$_5$ space-time. Our model satisfactorily fits the observational data for the low redshift sample of the experimental measurement of the Hubble parameter, which resulted in $H_0=72.2^{+5.3}_{-5.5}$km s$^{-1}$ Mpc$^{-1}$. |
gr-qc/0610018 | Max Niedermaier | M. Niedermaier | The Asymptotic Safety Scenario in Quantum Gravity -- An Introduction | 77p, 1 figure; v2: revised and updated; discussion of perturbation
theory in higher derivative theories extended. To appear as topical review in
CQG | Class.Quant.Grav.24:R171-230,2007 | 10.1088/0264-9381/24/18/R01 | null | gr-qc | null | The asymptotic safety scenario in quantum gravity is reviewed, according to
which a renormalizable quantum theory of the gravitational field is feasible
which reconciles asymptotically safe couplings with unitarity. All presently
known evidence is surveyed: (a) from the 2+\eps expansion, (b) from the
perturbation theory of higher derivative gravity theories and a `large N'
expansion in the number of matter fields, (c) from the 2-Killing vector
reduction, and (d) from truncated flow equations for the effective average
action. Special emphasis is given to the role of perturbation theory as a guide
to `asymptotic safety'. Further it is argued that as a consequence of the
scenario the selfinteractions appear two-dimensional in the extreme
ultraviolet. Two appendices discuss the distinct roles of the ultraviolet
renormalization in perturbation theory and in the flow equation formalism.
| [
{
"created": "Thu, 5 Oct 2006 10:09:13 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Jul 2007 09:51:40 GMT",
"version": "v2"
}
] | 2010-11-02 | [
[
"Niedermaier",
"M.",
""
]
] | The asymptotic safety scenario in quantum gravity is reviewed, according to which a renormalizable quantum theory of the gravitational field is feasible which reconciles asymptotically safe couplings with unitarity. All presently known evidence is surveyed: (a) from the 2+\eps expansion, (b) from the perturbation theory of higher derivative gravity theories and a `large N' expansion in the number of matter fields, (c) from the 2-Killing vector reduction, and (d) from truncated flow equations for the effective average action. Special emphasis is given to the role of perturbation theory as a guide to `asymptotic safety'. Further it is argued that as a consequence of the scenario the selfinteractions appear two-dimensional in the extreme ultraviolet. Two appendices discuss the distinct roles of the ultraviolet renormalization in perturbation theory and in the flow equation formalism. |
2006.06190 | Raihaneh Moti | R. Moti and A. Shojai (Tehran U.) | Traversability of quantum improved wormhole solution | 23 pages, 8 Figures | Phys.Rev. D101 (2020) no.12, 124042 | 10.1103/PhysRevD.101.124042 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We have investigated the problem of traversability of wormholes in the
framework of quantum improvement of gravity theory arising from functional
renormalization group methods to describe the asymptotic safe quantum gravity.
We have shown that improved pseudospherical wormholes could be traversable with
non--exotic matter, while spherical ones could not. This is done within a
specific model of improvement.
| [
{
"created": "Thu, 11 Jun 2020 04:47:40 GMT",
"version": "v1"
},
{
"created": "Mon, 22 Jun 2020 15:09:14 GMT",
"version": "v2"
}
] | 2020-07-14 | [
[
"Moti",
"R.",
"",
"Tehran U."
],
[
"Shojai",
"A.",
"",
"Tehran U."
]
] | We have investigated the problem of traversability of wormholes in the framework of quantum improvement of gravity theory arising from functional renormalization group methods to describe the asymptotic safe quantum gravity. We have shown that improved pseudospherical wormholes could be traversable with non--exotic matter, while spherical ones could not. This is done within a specific model of improvement. |
gr-qc/9610043 | Peter Leifer | Peter Leifer | Quantum theory requires gravity and superrelativity | 18 pages, Abstract, Proceeding of the Conference `Quantum Structure
'96, Berlin (1996) | null | null | TAUP 2357-1966 | gr-qc | null | The ordinary quantum theory points out that general relativity is negligible
for spatial distances up to the Planck scale. Consistency in the foundations of
the quantum theory requires a``soft'' spacetime structure of the general
relativity at essentially longer length. However, for some reasons this appears
to be not enough. A new framework (``superrelativity'') for the desirable
generalization of the foundation of quantum theory is proposed. A generalized
non-linear Klein-Gordon equation has been derived in order to shape a stable
wave packet.
| [
{
"created": "Sun, 20 Oct 1996 21:02:31 GMT",
"version": "v1"
}
] | 2012-09-13 | [
[
"Leifer",
"Peter",
""
]
] | The ordinary quantum theory points out that general relativity is negligible for spatial distances up to the Planck scale. Consistency in the foundations of the quantum theory requires a``soft'' spacetime structure of the general relativity at essentially longer length. However, for some reasons this appears to be not enough. A new framework (``superrelativity'') for the desirable generalization of the foundation of quantum theory is proposed. A generalized non-linear Klein-Gordon equation has been derived in order to shape a stable wave packet. |
1706.01753 | Singh Ibungochouba Telem | T. Ibungochouba Singh, I. Ablu Meitei and K. Yugindro Singh | Quantum gravity effects on Hawking radiation of Schwarzschild-de Sitter
black holes | Accepted in International Journal of Theoretical Physics | null | null | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The correction of Hawking temperature of Schwarzschild-de Sitter (SdS) black
hole is investigated using the generalized Klein-Gordon equation and the
generalized Dirac equation by taking the quantum gravity effects into account.
We derive the corrected Hawking temperatures for scalar particles and fermions
crossing the event horizon. The quantum gravity effects prevent the rise of
temperature in the SdS black hole. Besides correction of Hawking temperature,
the Hawking radiation of SdS black hole is also investigated using massive
particles tunneling method. By considering self gravitation effect of the
emitted particles and the space time background to be dynamical, it is also
shown that the tunneling rate is related to the change of Bekenstein-Hawking
entropy and small correction term $(1+2\beta m^2)$. If the energy and the
angular momentum are taken to be conserved, the derived emission spectrum
deviates from the pure thermal spectrum. This result gives a correction to the
Hawking radiation and is also in agreement with the result of Parikh and
Wilczek.
| [
{
"created": "Sat, 3 Jun 2017 10:59:22 GMT",
"version": "v1"
}
] | 2017-06-07 | [
[
"Singh",
"T. Ibungochouba",
""
],
[
"Meitei",
"I. Ablu",
""
],
[
"Singh",
"K. Yugindro",
""
]
] | The correction of Hawking temperature of Schwarzschild-de Sitter (SdS) black hole is investigated using the generalized Klein-Gordon equation and the generalized Dirac equation by taking the quantum gravity effects into account. We derive the corrected Hawking temperatures for scalar particles and fermions crossing the event horizon. The quantum gravity effects prevent the rise of temperature in the SdS black hole. Besides correction of Hawking temperature, the Hawking radiation of SdS black hole is also investigated using massive particles tunneling method. By considering self gravitation effect of the emitted particles and the space time background to be dynamical, it is also shown that the tunneling rate is related to the change of Bekenstein-Hawking entropy and small correction term $(1+2\beta m^2)$. If the energy and the angular momentum are taken to be conserved, the derived emission spectrum deviates from the pure thermal spectrum. This result gives a correction to the Hawking radiation and is also in agreement with the result of Parikh and Wilczek. |
2408.05893 | Nicolas R. Bertini | Nicolas R. Bertini | Scale-dependent gravity and covariant scale-setting | 17 pages | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | A fundamental element of scale-dependent gravity is the scale-setting
procedure. We present a new covariant expression to set the scale that arises
when examining the field equations. Considering the renormalization group
equations and imposing energy-momentum tensor conservation, we arrive at two
models of running of the gravitational and cosmological constants. In the
cosmological setting, we found that in one model the Big Bang singularity is
avoided, while in the other the Hubble tension can be alleviated. At the level
of cosmological perturbations, we derived the basic solutions and qualitatively
discussed the impacts of this scenario on structure formation.
| [
{
"created": "Mon, 12 Aug 2024 02:11:20 GMT",
"version": "v1"
}
] | 2024-08-13 | [
[
"Bertini",
"Nicolas R.",
""
]
] | A fundamental element of scale-dependent gravity is the scale-setting procedure. We present a new covariant expression to set the scale that arises when examining the field equations. Considering the renormalization group equations and imposing energy-momentum tensor conservation, we arrive at two models of running of the gravitational and cosmological constants. In the cosmological setting, we found that in one model the Big Bang singularity is avoided, while in the other the Hubble tension can be alleviated. At the level of cosmological perturbations, we derived the basic solutions and qualitatively discussed the impacts of this scenario on structure formation. |
1512.03227 | Kemal G\"ultekin | Kemal Gultekin | Affine Dynamics with Torsion | 25 pages, typos corrected | Eur. Phys. J. C (2016) 76:164 | 10.1140/epjc/s10052-016-4015-y | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this study, we give a thorough analysis of a general affine gravity with
torsion. After a brief exposition of the affine gravities considered by
Eddington and Schr\"{o}dinger, we construct and analyze different affine
gravities based on the determinants of the Ricci tensor, the torsion tensor,
the Riemann tensor and their combinations. In each case we reduce equations of
motion to their simplest forms and give a detailed analysis of their solutions.
Our analyses lead to the construction of the affine connection in terms of the
curvature and torsion tensors. Our solutions of the dynamical equations show
that the curvature tensors at different points are correlated via non-local,
exponential rescaling factors determined by the torsion tensor.
| [
{
"created": "Thu, 10 Dec 2015 12:16:10 GMT",
"version": "v1"
},
{
"created": "Sun, 3 Apr 2016 00:48:23 GMT",
"version": "v2"
}
] | 2016-04-05 | [
[
"Gultekin",
"Kemal",
""
]
] | In this study, we give a thorough analysis of a general affine gravity with torsion. After a brief exposition of the affine gravities considered by Eddington and Schr\"{o}dinger, we construct and analyze different affine gravities based on the determinants of the Ricci tensor, the torsion tensor, the Riemann tensor and their combinations. In each case we reduce equations of motion to their simplest forms and give a detailed analysis of their solutions. Our analyses lead to the construction of the affine connection in terms of the curvature and torsion tensors. Our solutions of the dynamical equations show that the curvature tensors at different points are correlated via non-local, exponential rescaling factors determined by the torsion tensor. |
gr-qc/0410040 | Chi Wai Lai | Chi-Wai Lai | A Numerical Study of Boson Stars | 168 pages, 54 figures, PhD Thesis. Positions of figures were
misplaced For a high resolution version, see
http://laplace.physics.ubc.ca/People/cwlai/papers/papers.html For | null | null | null | gr-qc | null | We present a numerical study of general relativistic boson stars in both
spherical symmetry and axisymmetry. We consider both time-independent problems,
involving the solution of equilibrium equations for rotating boson stars, and
time-dependent problems, focusing on black hole critical behaviour associated
with boson stars.
The study of the critical phenomena that arise at the threshold of black hole
formation has been a subject of intense interest among relativists and applied
mathematicians over the past decade. Type I critical phenomena were previously
observed in the dynamics of spherically symmetric boson stars by Hawley and
Choptuik. We extend this work and show that, contrary to previous claims, the
subcritical end-state is well described by a stable boson star executing a
large amplitude oscillation with a frequency in good agreement with that
predicted for the fundamental normal mode of the end-state star from linear
perturbation theory.
We then extend our studies of critical phenomena to the axisymmetric case,
studying two distinct classes of parametrized families of initial data whose
evolution generates families of spacetimes that ``interpolate'' between those
than contain a black hole and those that do not. In both cases we find strong
evidence for a Type I transition at threshold, and are able to demonstrate
scaling of the lifetime for near-critical configurations of the type expected
for such a transition. This is the first time that Type I critical solutions
have been simulated in axisymmetry.
| [
{
"created": "Fri, 8 Oct 2004 14:30:20 GMT",
"version": "v1"
},
{
"created": "Mon, 11 Oct 2004 13:29:40 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Lai",
"Chi-Wai",
""
]
] | We present a numerical study of general relativistic boson stars in both spherical symmetry and axisymmetry. We consider both time-independent problems, involving the solution of equilibrium equations for rotating boson stars, and time-dependent problems, focusing on black hole critical behaviour associated with boson stars. The study of the critical phenomena that arise at the threshold of black hole formation has been a subject of intense interest among relativists and applied mathematicians over the past decade. Type I critical phenomena were previously observed in the dynamics of spherically symmetric boson stars by Hawley and Choptuik. We extend this work and show that, contrary to previous claims, the subcritical end-state is well described by a stable boson star executing a large amplitude oscillation with a frequency in good agreement with that predicted for the fundamental normal mode of the end-state star from linear perturbation theory. We then extend our studies of critical phenomena to the axisymmetric case, studying two distinct classes of parametrized families of initial data whose evolution generates families of spacetimes that ``interpolate'' between those than contain a black hole and those that do not. In both cases we find strong evidence for a Type I transition at threshold, and are able to demonstrate scaling of the lifetime for near-critical configurations of the type expected for such a transition. This is the first time that Type I critical solutions have been simulated in axisymmetry. |
gr-qc/0201037 | Jan Czerniawski | J. Czerniawski | What is wrong with Schwarzschild's coordinates? | LaTeX, 4 1/2 pages; the order of assumptions changed and new
references added | Concepts Phys. 3 (2006) 307-318 | null | null | gr-qc | null | A strict derivation of the Schwarzschild metric, based solely on Newton's law
of free fall and the equivalence principle, is presented. In the light of it,
regarding Schwarzschild's coordinates as representing the point of view of a
distant observer resting relative to the source of a centrally symmetric
gravitational field, proves illegitimate. Such point of view is better
represented by the Painleve-Gullstrand system of coordinates, which agrees with
Schwarzschild's system with respect to its spatial coordinates and time scale,
but disagrees with respect to the relation of simultaneity. A duality of the
Schwarzschild solution and its time-irreversibility is suggested. The physical
meaning of the coordinate singularity at the Schwarzschild radius is clarified.
| [
{
"created": "Fri, 11 Jan 2002 08:16:31 GMT",
"version": "v1"
},
{
"created": "Sat, 12 Jan 2002 15:06:15 GMT",
"version": "v2"
},
{
"created": "Wed, 11 Sep 2002 14:23:52 GMT",
"version": "v3"
},
{
"created": "Fri, 12 Nov 2004 12:03:19 GMT",
"version": "v4"
}
] | 2007-05-23 | [
[
"Czerniawski",
"J.",
""
]
] | A strict derivation of the Schwarzschild metric, based solely on Newton's law of free fall and the equivalence principle, is presented. In the light of it, regarding Schwarzschild's coordinates as representing the point of view of a distant observer resting relative to the source of a centrally symmetric gravitational field, proves illegitimate. Such point of view is better represented by the Painleve-Gullstrand system of coordinates, which agrees with Schwarzschild's system with respect to its spatial coordinates and time scale, but disagrees with respect to the relation of simultaneity. A duality of the Schwarzschild solution and its time-irreversibility is suggested. The physical meaning of the coordinate singularity at the Schwarzschild radius is clarified. |
1304.8106 | Tim Johannsen | Tim Johannsen (Waterloo, CITA, Perimeter) | Inner Accretion Disk Edges in a Kerr-Like Spacetime | 13 pages, 10 figures, accepted for publication in PRD, published
version | null | 10.1103/PhysRevD.87.124010 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | According to the no-hair theorem, astrophysical black holes are uniquely
described by the Kerr metric. In order to test this theorem with observations
in either the electromagnetic or gravitational-wave spectra, several Kerr-like
spacetimes have been constructed which describe potential deviations from the
Kerr spacetime in parametric form. For electromagnetic tests of the no-hair
theorem, such metrics allow for the proper modeling of the accretion flows
around candidate black holes and the radiation emitted from them. In many of
these models, the location of the inner edge of the accretion disk is of
special importance. This inner edge is often taken to coincide with the
innermost stable circular orbit, which can serve as a direct probe of the spin
and the deviation from the Kerr metric. In certain cases, however, an innermost
stable circular orbit does not exist, and the inner edge of an accretion disk
is instead determined by an instability against small perturbations in the
direction vertical to the disk. In this paper, I analyze the properties of
accretion disks in the Kerr-like metric proposed by Johannsen and Psaltis
[Phys. Rev. D 83, 124015 (2011)], whose inner edges are located at the radii
where this vertical instability occurs. I derive expressions of the energy and
axial angular momentum of disk particles that move on circular equatorial
orbits and calculate the locations of the inner disk edges. As a possible
observable of such accretion disks, I simulate profiles of relativistically
broadened iron lines and show that they depend significantly on the values of
the spin and the deviation parameter.
| [
{
"created": "Tue, 30 Apr 2013 18:36:57 GMT",
"version": "v1"
},
{
"created": "Thu, 2 May 2013 18:57:42 GMT",
"version": "v2"
},
{
"created": "Fri, 24 May 2013 13:37:34 GMT",
"version": "v3"
},
{
"created": "Thu, 6 Jun 2013 14:04:23 GMT",
"version": "v4"
}
] | 2015-06-15 | [
[
"Johannsen",
"Tim",
"",
"Waterloo, CITA, Perimeter"
]
] | According to the no-hair theorem, astrophysical black holes are uniquely described by the Kerr metric. In order to test this theorem with observations in either the electromagnetic or gravitational-wave spectra, several Kerr-like spacetimes have been constructed which describe potential deviations from the Kerr spacetime in parametric form. For electromagnetic tests of the no-hair theorem, such metrics allow for the proper modeling of the accretion flows around candidate black holes and the radiation emitted from them. In many of these models, the location of the inner edge of the accretion disk is of special importance. This inner edge is often taken to coincide with the innermost stable circular orbit, which can serve as a direct probe of the spin and the deviation from the Kerr metric. In certain cases, however, an innermost stable circular orbit does not exist, and the inner edge of an accretion disk is instead determined by an instability against small perturbations in the direction vertical to the disk. In this paper, I analyze the properties of accretion disks in the Kerr-like metric proposed by Johannsen and Psaltis [Phys. Rev. D 83, 124015 (2011)], whose inner edges are located at the radii where this vertical instability occurs. I derive expressions of the energy and axial angular momentum of disk particles that move on circular equatorial orbits and calculate the locations of the inner disk edges. As a possible observable of such accretion disks, I simulate profiles of relativistically broadened iron lines and show that they depend significantly on the values of the spin and the deviation parameter. |
1712.10268 | Alan Kostelecky | Alan Kostelecky, Matthew Mewes | Lorentz and Diffeomorphism Violations in Linearized Gravity | 17 pages | Phys.Lett.B779: 136-142, 2018 | 10.1016/j.physletb.2018.01.082 | IUHET 626 | gr-qc astro-ph.HE hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Lorentz and diffeomorphism violations are studied in linearized gravity using
effective field theory. A classification of all gauge-invariant and
gauge-violating terms is given. The exact covariant dispersion relation for
gravitational modes involving operators of arbitrary mass dimension is
constructed, and various special limits are discussed.
| [
{
"created": "Fri, 29 Dec 2017 16:20:20 GMT",
"version": "v1"
}
] | 2018-02-23 | [
[
"Kostelecky",
"Alan",
""
],
[
"Mewes",
"Matthew",
""
]
] | Lorentz and diffeomorphism violations are studied in linearized gravity using effective field theory. A classification of all gauge-invariant and gauge-violating terms is given. The exact covariant dispersion relation for gravitational modes involving operators of arbitrary mass dimension is constructed, and various special limits are discussed. |
2005.10268 | Shahar Hod | Shahar Hod | Reissner-Nordstr\"om black holes supporting non-minimally coupled
massive scalar field configurations | 7 pages | Physical Review D 101, 104025 (2020) | 10.1103/PhysRevD.101.104025 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has recently been demonstrated that static spatially regular scalar
fields, which are non-minimally coupled to the electromagnetic field of a
charged central black hole, can be supported in the exterior regions of the
black-hole spacetime. In the present paper we use {\it analytical} techniques
in order to study the physical and mathematical properties of the externally
supported linearized scalar field configurations (scalar 'clouds') in the
dimensionless large-mass regime $\mu r_+\gg1$ (here $\mu$ and $r_+$ are
respectively the proper mass of the supported scalar field and the outer
horizon radius of the central supporting black hole). In particular, we derive
a remarkably compact analytical formula for the discrete resonant spectrum
$\{\alpha_n(\mu;Q/M)\}_{n=0}^{n=\infty}$ which characterizes the dimensionless
coupling parameter of the composed
black-hole-non-minimally-coupled-linearized-massive-scalar-field
configurations. The physical significance of this resonant spectrum stems from
the fact that, for a given value of the dimensionless black-hole electric
charge $Q/M$, the fundamental (smallest) eigenvalue $\alpha_0(\mu)$ determines
the critical existence-line of the composed black-hole-massive-field system, a
boundary line which separates non-linearly coupled hairy
charged-black-hole-massive-scalar-field configurations from bald
Reissner-Nordstr\"om black holes. The analytical results derived in this paper
are confirmed by direct numerical computations.
| [
{
"created": "Wed, 20 May 2020 18:00:09 GMT",
"version": "v1"
}
] | 2020-05-27 | [
[
"Hod",
"Shahar",
""
]
] | It has recently been demonstrated that static spatially regular scalar fields, which are non-minimally coupled to the electromagnetic field of a charged central black hole, can be supported in the exterior regions of the black-hole spacetime. In the present paper we use {\it analytical} techniques in order to study the physical and mathematical properties of the externally supported linearized scalar field configurations (scalar 'clouds') in the dimensionless large-mass regime $\mu r_+\gg1$ (here $\mu$ and $r_+$ are respectively the proper mass of the supported scalar field and the outer horizon radius of the central supporting black hole). In particular, we derive a remarkably compact analytical formula for the discrete resonant spectrum $\{\alpha_n(\mu;Q/M)\}_{n=0}^{n=\infty}$ which characterizes the dimensionless coupling parameter of the composed black-hole-non-minimally-coupled-linearized-massive-scalar-field configurations. The physical significance of this resonant spectrum stems from the fact that, for a given value of the dimensionless black-hole electric charge $Q/M$, the fundamental (smallest) eigenvalue $\alpha_0(\mu)$ determines the critical existence-line of the composed black-hole-massive-field system, a boundary line which separates non-linearly coupled hairy charged-black-hole-massive-scalar-field configurations from bald Reissner-Nordstr\"om black holes. The analytical results derived in this paper are confirmed by direct numerical computations. |
2104.02067 | D. C. Robinson | D. C. Robinson | Spinorial coordinates for Lorentzian 4-metrics | Equations added. Final section re-written | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Lorentzian 4-metrics are expressed in spinorial coordinates. In these
coordinates the metric components can be factorized into a product of complex
conjugate quantities. The linearized theory and Einstein's vacuum field
equations are studied using these coordinates. The relationship between
Lorentzian and complex 4-metrics is discussed.
| [
{
"created": "Mon, 5 Apr 2021 16:03:14 GMT",
"version": "v1"
},
{
"created": "Sun, 10 Oct 2021 14:58:07 GMT",
"version": "v2"
}
] | 2021-10-12 | [
[
"Robinson",
"D. C.",
""
]
] | Lorentzian 4-metrics are expressed in spinorial coordinates. In these coordinates the metric components can be factorized into a product of complex conjugate quantities. The linearized theory and Einstein's vacuum field equations are studied using these coordinates. The relationship between Lorentzian and complex 4-metrics is discussed. |
gr-qc/0307050 | Niall \'O Murchadha | Niall \'O Murchadha, Krzysztof Roszkowski | Embedding spherical spacelike slices in a Schwarzschild solution | null | Class.Quant.Grav. 23 (2006) 539-548 | 10.1088/0264-9381/23/2/017 | null | gr-qc | null | Given a spherical spacelike three-geometry, there exists a very simple
algebraic condition which tells us whether, and in which, Schwarzschild
solution this geometry can be smoothly embedded. One can use this result to
show that any given Schwarzschild solution covers a significant subset of
spherical superspace and these subsets form a sequence of nested domains as the
Schwarzschild mass increases. This also demonstrates that spherical data offer
an immediate counter example to the thick sandwich `theorem'.
| [
{
"created": "Thu, 10 Jul 2003 13:42:15 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Murchadha",
"Niall Ó",
""
],
[
"Roszkowski",
"Krzysztof",
""
]
] | Given a spherical spacelike three-geometry, there exists a very simple algebraic condition which tells us whether, and in which, Schwarzschild solution this geometry can be smoothly embedded. One can use this result to show that any given Schwarzschild solution covers a significant subset of spherical superspace and these subsets form a sequence of nested domains as the Schwarzschild mass increases. This also demonstrates that spherical data offer an immediate counter example to the thick sandwich `theorem'. |
1205.3481 | Manuel Rodrigues | Manuel E. Rodrigues, Deborah F. Jardim, M. J. S. Houndjo and Ratbay
Myrzakulov | Thermodynamics of black plane solution | 19 pages, 3 figures, version accepted for publication in General
Relativity and Gravitation | General Relativity and Gravitation, v.45, N11, 2309-2323 (2013) | 10.1007/s10714-013-1585-y | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We obtain a new phantom black plane solution in 4D of the Einstein-Maxwell
theory coupled with a cosmological constant. We analyse their basic properties,
as well as its causal structure, and obtain the extensive and intensive
thermodynamic variables, as well as the specific heat and the first law.
Through the specific heat and the so-called geometric methods, we analyse in
detail their thermodynamic properties, the extreme and phase transition limits,
as well as the local and global stabilities of the system. The normal case is
shown with an extreme limit and the phantom one with a phase transition only
for null mass, which is physically inaccessible. The systems present local and
global stabilities for certain values of the entropy density with respect to
the electric charge, for the canonical and grand canonical ensembles.
| [
{
"created": "Tue, 15 May 2012 19:38:05 GMT",
"version": "v1"
},
{
"created": "Thu, 22 Nov 2012 11:52:00 GMT",
"version": "v2"
},
{
"created": "Mon, 12 Aug 2013 23:56:13 GMT",
"version": "v3"
}
] | 2013-10-30 | [
[
"Rodrigues",
"Manuel E.",
""
],
[
"Jardim",
"Deborah F.",
""
],
[
"Houndjo",
"M. J. S.",
""
],
[
"Myrzakulov",
"Ratbay",
""
]
] | We obtain a new phantom black plane solution in 4D of the Einstein-Maxwell theory coupled with a cosmological constant. We analyse their basic properties, as well as its causal structure, and obtain the extensive and intensive thermodynamic variables, as well as the specific heat and the first law. Through the specific heat and the so-called geometric methods, we analyse in detail their thermodynamic properties, the extreme and phase transition limits, as well as the local and global stabilities of the system. The normal case is shown with an extreme limit and the phantom one with a phase transition only for null mass, which is physically inaccessible. The systems present local and global stabilities for certain values of the entropy density with respect to the electric charge, for the canonical and grand canonical ensembles. |
2401.10410 | Piyabut Burikham | Muhammad F. A. R. Sakti, Piyabut Burikham, Tiberiu Harko | Thermodynamics of the Weyl Geometric Gravity Black Holes | 19 pages, 14 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by-sa/4.0/ | We consider the thermodynamic properties of an exact black hole solution
obtained in Weyl geometric gravity theory, by considering the simplest
conformally invariant action, constructed from the square of the Weyl scalar,
and the strength of the Weyl vector only. The action is linearized in the Weyl
scalar by introducing an auxiliary scalar field, and thus it can be
reformulated as a scalar-vector-tensor theory in a Riemann space, in the
presence of a nonminimal coupling between the Ricci scalar and the scalar
field. In static spherical symmetry, this theory admits an exact black hole
solution, which generalizes the standard Schwarzschild-de Sitter solution
through the presence of two new terms in the metric, having a linear and a
quadratic dependence on the radial coordinate, respectively. The solution is
obtained by assuming that the Weyl vector has only a radial component. After
studying the locations of the event and cosmological horizons of the Weyl
geometric black hole, we investigate in detail the thermodynamical (quantum
properties) of this type of black holes, by considering the Hawking
temperature, the entropy, specific heat and the Helmholtz free energy functions
on both the event and the cosmological horizons. The Weyl geometric black holes
have thermodynamic properties that clearly differentiate them from similar
solutions of other modified gravity theories. The obtained results may lead to
the possibility of a better understanding of the properties of the black holes
in alternative gravity, and of the relevance of the thermodynamic aspects in
black hole physics.
| [
{
"created": "Thu, 18 Jan 2024 22:37:22 GMT",
"version": "v1"
},
{
"created": "Fri, 2 Aug 2024 16:52:58 GMT",
"version": "v2"
}
] | 2024-08-05 | [
[
"Sakti",
"Muhammad F. A. R.",
""
],
[
"Burikham",
"Piyabut",
""
],
[
"Harko",
"Tiberiu",
""
]
] | We consider the thermodynamic properties of an exact black hole solution obtained in Weyl geometric gravity theory, by considering the simplest conformally invariant action, constructed from the square of the Weyl scalar, and the strength of the Weyl vector only. The action is linearized in the Weyl scalar by introducing an auxiliary scalar field, and thus it can be reformulated as a scalar-vector-tensor theory in a Riemann space, in the presence of a nonminimal coupling between the Ricci scalar and the scalar field. In static spherical symmetry, this theory admits an exact black hole solution, which generalizes the standard Schwarzschild-de Sitter solution through the presence of two new terms in the metric, having a linear and a quadratic dependence on the radial coordinate, respectively. The solution is obtained by assuming that the Weyl vector has only a radial component. After studying the locations of the event and cosmological horizons of the Weyl geometric black hole, we investigate in detail the thermodynamical (quantum properties) of this type of black holes, by considering the Hawking temperature, the entropy, specific heat and the Helmholtz free energy functions on both the event and the cosmological horizons. The Weyl geometric black holes have thermodynamic properties that clearly differentiate them from similar solutions of other modified gravity theories. The obtained results may lead to the possibility of a better understanding of the properties of the black holes in alternative gravity, and of the relevance of the thermodynamic aspects in black hole physics. |
1503.04197 | Dr. Sudhaker Upadhyay | Sudhaker Upadhyay | Field-dependent symmetries in Friedmann-Robertson-Walker models | 7 pages, No figure, Accepted in Annals of Physics (Journal version) | Annals of Physics 356 (2015) 299-305 | 10.1016/j.aop.2015.03.002 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider effective actions of the cosmological Friedmann-Robertson-Walker
(FRW) models and discuss their fermionic rigid BRST invariance. Further, we
demonstrate the finite field-dependent BRST transformations as a limiting case
of continuous field-dependent BRST transformations described in terms of
continuous parameter $\kappa$. The Jacobian under such finite field-dependent
BRST transformations is computed explicitly, which amounts an extra piece in
the effective action within functional integral. We show that for a particular
choice of the parameter the finite field-dependent BRST transformation maps the
generating functional for FRW models from one gauge to another.
| [
{
"created": "Fri, 13 Mar 2015 10:04:31 GMT",
"version": "v1"
},
{
"created": "Tue, 17 Mar 2015 11:45:55 GMT",
"version": "v2"
}
] | 2015-04-02 | [
[
"Upadhyay",
"Sudhaker",
""
]
] | We consider effective actions of the cosmological Friedmann-Robertson-Walker (FRW) models and discuss their fermionic rigid BRST invariance. Further, we demonstrate the finite field-dependent BRST transformations as a limiting case of continuous field-dependent BRST transformations described in terms of continuous parameter $\kappa$. The Jacobian under such finite field-dependent BRST transformations is computed explicitly, which amounts an extra piece in the effective action within functional integral. We show that for a particular choice of the parameter the finite field-dependent BRST transformation maps the generating functional for FRW models from one gauge to another. |
gr-qc/9501009 | Sardanashvily Gennadi | G.Sardanashvily (Dept of Theoretical Physics, Moscow State Univ) | Energy-Momentum Conservation Laws in Affine-Metric Gravitation Theory | 20 pp, LaTeX file | null | null | TP\95\001 | gr-qc | null | The Lagrangian formulation of field theory does not provide any universal
energy-momentum conservation law in order to analize that in gravitation
theory. In Lagrangian field theory, we get different identities involving
different stress energy-momentum tensors which however are not conserved,
otherwise in the covariant multimomentum Hamiltonian formalism. In the
framework of this formalism, we have the fundamental identity whose restriction
to a constraint space can be treated the energy-momentum transformation law.
This identity remains true also for gravity. Thus, the tools are at hand to
investigate the energy-momentum conservation laws in gravitation theory. The
key point consists in the feature of a metric gravitational field whose
canonical momenta on the constraint space are equal to zero.
| [
{
"created": "Tue, 10 Jan 1995 01:11:37 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Sardanashvily",
"G.",
"",
"Dept of Theoretical Physics, Moscow State Univ"
]
] | The Lagrangian formulation of field theory does not provide any universal energy-momentum conservation law in order to analize that in gravitation theory. In Lagrangian field theory, we get different identities involving different stress energy-momentum tensors which however are not conserved, otherwise in the covariant multimomentum Hamiltonian formalism. In the framework of this formalism, we have the fundamental identity whose restriction to a constraint space can be treated the energy-momentum transformation law. This identity remains true also for gravity. Thus, the tools are at hand to investigate the energy-momentum conservation laws in gravitation theory. The key point consists in the feature of a metric gravitational field whose canonical momenta on the constraint space are equal to zero. |
gr-qc/0201030 | null | John C. Baez and S. Jay Olson | Uncertainty in Measurements of Distance | 5 pages LaTeX | Class.Quant.Grav.19:L121-L126,2002 | 10.1088/0264-9381/19/14/101 | null | gr-qc | null | Ng and van Dam have argued that quantum theory and general relativity give a
lower bound of L^{1/3} L_P^{2/3} on the uncertainty of any distance, where L is
the distance to be measured and L_P is the Planck length. Their idea is roughly
that to minimize the position uncertainty of a freely falling measuring device
one must increase its mass, but if its mass becomes too large it will collapse
to form a black hole. Here we show that one can go below the Ng-van Dam bound
by attaching the measuring device to a massive elastic rod. Relativistic
limitations on the rod's rigidity, together with the constraint that its length
exceeds its Schwarzschild radius, imply that zero-point fluctuations of the rod
give an uncertainty greater than or equal to L_P.
| [
{
"created": "Wed, 9 Jan 2002 23:39:18 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Baez",
"John C.",
""
],
[
"Olson",
"S. Jay",
""
]
] | Ng and van Dam have argued that quantum theory and general relativity give a lower bound of L^{1/3} L_P^{2/3} on the uncertainty of any distance, where L is the distance to be measured and L_P is the Planck length. Their idea is roughly that to minimize the position uncertainty of a freely falling measuring device one must increase its mass, but if its mass becomes too large it will collapse to form a black hole. Here we show that one can go below the Ng-van Dam bound by attaching the measuring device to a massive elastic rod. Relativistic limitations on the rod's rigidity, together with the constraint that its length exceeds its Schwarzschild radius, imply that zero-point fluctuations of the rod give an uncertainty greater than or equal to L_P. |
2304.13603 | Misbah Shahzadi | Martin Kolo\v{s}, Misbah Shahzadi, Arman Tursunov | Charged particle dynamics in parabolic magnetosphere around
Schwarzschild black hole | 23 pages, 16 figures | Eur. Phys. J. C (2023) 83:323 | 10.1140/epjc/s10052-023-11498-8 | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | The study of charged particle dynamics in the combined gravitational and
magnetic field can provide important theoretical insight into astrophysical
processes around black holes. In this paper, we explore the charged particle
dynamics in parabolic magnetic field configuration around Schwarzschild black
hole, since the paraboloidal shapes of magnetic field lines around black holes
are well motivated by the numerical simulations and supported by observations
of relativistic jets. Analysing the stability of bounded orbits and using the
effective potential approach, we show the possibility of existence of stable
circular off-equatorial orbits around the symmetry axis. We also show the
influence of radiation reaction force on the dynamics of charged particles, in
particular on the chaoticity of the motion and Poincar\'{e} sections,
oscillatory frequencies, and emitted electromagnetic spectrum. Applied to
Keplerian accretion disks, we show that in parabolic magnetic field
configuration, the thin accretion configurations can be either destroyed or
transformed into a thick toroidal structure given the radiation reaction and
electromagnetic-disk interactions included. Calculating the Fourier spectra for
radiating charged particle trajectories, we find that the radiation reaction
force does not affect the main frequency peaks, however, it lowers the higher
harmonics making the spectrum more flat and diluted in high frequency range.
| [
{
"created": "Wed, 26 Apr 2023 14:57:46 GMT",
"version": "v1"
}
] | 2024-03-19 | [
[
"Kološ",
"Martin",
""
],
[
"Shahzadi",
"Misbah",
""
],
[
"Tursunov",
"Arman",
""
]
] | The study of charged particle dynamics in the combined gravitational and magnetic field can provide important theoretical insight into astrophysical processes around black holes. In this paper, we explore the charged particle dynamics in parabolic magnetic field configuration around Schwarzschild black hole, since the paraboloidal shapes of magnetic field lines around black holes are well motivated by the numerical simulations and supported by observations of relativistic jets. Analysing the stability of bounded orbits and using the effective potential approach, we show the possibility of existence of stable circular off-equatorial orbits around the symmetry axis. We also show the influence of radiation reaction force on the dynamics of charged particles, in particular on the chaoticity of the motion and Poincar\'{e} sections, oscillatory frequencies, and emitted electromagnetic spectrum. Applied to Keplerian accretion disks, we show that in parabolic magnetic field configuration, the thin accretion configurations can be either destroyed or transformed into a thick toroidal structure given the radiation reaction and electromagnetic-disk interactions included. Calculating the Fourier spectra for radiating charged particle trajectories, we find that the radiation reaction force does not affect the main frequency peaks, however, it lowers the higher harmonics making the spectrum more flat and diluted in high frequency range. |
gr-qc/0510114 | Janusz Garecki Dr. | Janusz Garecki | The averaged tensors of the relative energy-momentum and angular
momentum in general relativity and some their applications | 30 pages, minor changes referring to Kasner universes | Found.Phys.37:341-365,2007 | 10.1007/s10701-007-9107-y | null | gr-qc | null | There exist at least a few different kind of averaging of the differences of
the energy-momentum and angular momentum in normal coordinates {\bf NC(P)}
which give tensorial quantities. The obtained averaged quantities are
equivalent mathematically because they differ only by constant scalar
dimensional factors. One of these averaging was used in our papers [1-8] giving
the {\it canonical superenergy and angular supermomentum tensors}.
In this paper we present another averaging of the differences of the
energy-momentum and angular momentum which gives tensorial quantities with
proper dimensions of the energy-momentum and angular momentum densities. But
these averaged relative energy-momentum and angular momentum tensors, closely
related to the canonical superenergy and angular supermomentum tensors, {\it
depend on some fundamental length $L>0$}.
The averaged relative energy-momentum and angular momentum tensors of the
gravitational field obtained in the paper can be applied, like the canonical
superenergy and angular supermomentum tensors, to {\it coordinate independent}
analysis (local and in special cases also global) of this field.
We have applied the averaged relative energy-momentum tensors to analyze
vacuum gravitational energy and momentum and to analyze energy and momentum of
the Friedman (and also more general) universes. The obtained results are very
interesting, e.g., the averaged relative energy density is {\it positive
definite} for the all Friedman universes.
| [
{
"created": "Wed, 26 Oct 2005 16:21:23 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Aug 2006 13:43:49 GMT",
"version": "v2"
},
{
"created": "Fri, 8 Sep 2006 10:25:57 GMT",
"version": "v3"
}
] | 2011-08-04 | [
[
"Garecki",
"Janusz",
""
]
] | There exist at least a few different kind of averaging of the differences of the energy-momentum and angular momentum in normal coordinates {\bf NC(P)} which give tensorial quantities. The obtained averaged quantities are equivalent mathematically because they differ only by constant scalar dimensional factors. One of these averaging was used in our papers [1-8] giving the {\it canonical superenergy and angular supermomentum tensors}. In this paper we present another averaging of the differences of the energy-momentum and angular momentum which gives tensorial quantities with proper dimensions of the energy-momentum and angular momentum densities. But these averaged relative energy-momentum and angular momentum tensors, closely related to the canonical superenergy and angular supermomentum tensors, {\it depend on some fundamental length $L>0$}. The averaged relative energy-momentum and angular momentum tensors of the gravitational field obtained in the paper can be applied, like the canonical superenergy and angular supermomentum tensors, to {\it coordinate independent} analysis (local and in special cases also global) of this field. We have applied the averaged relative energy-momentum tensors to analyze vacuum gravitational energy and momentum and to analyze energy and momentum of the Friedman (and also more general) universes. The obtained results are very interesting, e.g., the averaged relative energy density is {\it positive definite} for the all Friedman universes. |
2309.01548 | Edoardo D'Angelo | Edoardo D'Angelo | Relative Entropy from Coherent States in Black Hole Thermodynamics and
Cosmology | Master Thesis, defended on July 2020 at the University of Genova.
Thesis supervisor: Nicola Pinamonti and Pierantonio Zangh\`i. Results on the
relative entropy for dynamical holes appeared generalised in a subsequent
paper | null | null | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The aim of this work is to study the role of relative entropy in the
thermodynamics of black holes and cosmological horizons. We adapt some recent
results on the relative entropy of coherent excitations of the vacuum, to find
the variation of generalised entropy of static and dynamical black holes and
for cosmological horizons.
We review the argument for static black holes by Hollands and Ishibashi
(2019) with simple modifications. We link the variation of relative entropy to
the growth of the horizon using a conservation law for the stress-energy
tensor, and we recover the known results. We then study the application of the
same framework to the case of dynamical horizons. We study in detail the case
of Vaidya spacetime, and we find that a notion of black hole entropy naturally
emerges, equals to one-fourth of the area of the dynamical horizon. In the case
of dynamical black holes we find an additional term, which is not present in
the static case, and that represents the work done on the black hole. We
finally show in a simple case that it is possible to follow the same scheme to
assign an entropy to the horizons emerging in cosmological scenarios.
| [
{
"created": "Mon, 4 Sep 2023 12:01:13 GMT",
"version": "v1"
}
] | 2023-09-06 | [
[
"D'Angelo",
"Edoardo",
""
]
] | The aim of this work is to study the role of relative entropy in the thermodynamics of black holes and cosmological horizons. We adapt some recent results on the relative entropy of coherent excitations of the vacuum, to find the variation of generalised entropy of static and dynamical black holes and for cosmological horizons. We review the argument for static black holes by Hollands and Ishibashi (2019) with simple modifications. We link the variation of relative entropy to the growth of the horizon using a conservation law for the stress-energy tensor, and we recover the known results. We then study the application of the same framework to the case of dynamical horizons. We study in detail the case of Vaidya spacetime, and we find that a notion of black hole entropy naturally emerges, equals to one-fourth of the area of the dynamical horizon. In the case of dynamical black holes we find an additional term, which is not present in the static case, and that represents the work done on the black hole. We finally show in a simple case that it is possible to follow the same scheme to assign an entropy to the horizons emerging in cosmological scenarios. |
1005.5442 | Llu\'is Bel | Ll. Bel | Local cosmology of the solar system | 6 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A time-dependent model of space-time is used to describe the gravitational
field of the sun. This model is a spherically symmetric approximate solution of
Einstein's equations in vacuum. Near the sun it approximates one of the models
derived from the Schwarzschild solution, while at large distances it becomes a
milne's-like zero space-time curvature model. Two local cosmology free
parameters provide simple descriptions for the secular increasing of the
astronomical unit, as well as the "anomalous" radial acceleration of the
Pioneer probe. We make also a comment about the possibility of deriving MOND's
phenomenology from General relativity.
| [
{
"created": "Sat, 29 May 2010 09:22:45 GMT",
"version": "v1"
}
] | 2010-06-01 | [
[
"Bel",
"Ll.",
""
]
] | A time-dependent model of space-time is used to describe the gravitational field of the sun. This model is a spherically symmetric approximate solution of Einstein's equations in vacuum. Near the sun it approximates one of the models derived from the Schwarzschild solution, while at large distances it becomes a milne's-like zero space-time curvature model. Two local cosmology free parameters provide simple descriptions for the secular increasing of the astronomical unit, as well as the "anomalous" radial acceleration of the Pioneer probe. We make also a comment about the possibility of deriving MOND's phenomenology from General relativity. |
0803.2642 | Alessandro Pesci | Alessandro Pesci | On the statistical-mechanical meaning of the Bousso bound | 6 pages. Some editing and the addition of a reference. This version,
ideally corresponding to the published one, contains 4 corrections to it,
with two of them (p.3, line 19 and p.6, line 10 of this version) with
semantic relevance | Class.Quant.Grav.25:125005,2008 | 10.1088/0264-9381/25/12/125005 | null | gr-qc cond-mat.stat-mech | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Bousso entropy bound, in its generalized form, is investigated for the
case of perfect fluids at local thermodynamic equilibrium and evidence is found
that the bound is satisfied if and only if a certain local thermodynamic
property holds, emerging when the attempt is made to apply the bound to thin
layers of matter. This property consists in the existence of an ultimate lower
limit l* to the thickness of the slices for which a statistical-mechanical
description is viable, depending l* on the thermodynamical variables which
define the state of the system locally. This limiting scale, found to be in
general much larger than the Planck scale (so that no Planck scale physics must
be necessarily invoked to justify it), appears not related to gravity and this
suggests that the generalized entropy bound is likely to be rooted on
conventional flat-spacetime statistical mechanics, with the maximum admitted
entropy being however actually determined also by gravity.
Some examples of ideal fluids are considered in order to identify the
mechanisms which can set a lower limit to the statistical-mechanical
description and these systems are found to respect the lower limiting scale l*.
The photon gas, in particular, appears to seemingly saturate this limiting
scale and the consequence is drawn that for systems consisting of a single
slice of a photon gas with thickness l*, the generalized Bousso bound is
saturated. It is argued that this seems to open the way to a peculiar
understanding of black hole entropy: if an entropy can meaningfully (i.e. with
a second law) be assigned to a black hole, the value A/4 for it (where A is the
area of the black hole) is required simply by (conventional) statistical
mechanics coupled to general relativity.
| [
{
"created": "Tue, 18 Mar 2008 16:10:21 GMT",
"version": "v1"
},
{
"created": "Wed, 4 Jun 2008 09:41:47 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Pesci",
"Alessandro",
""
]
] | The Bousso entropy bound, in its generalized form, is investigated for the case of perfect fluids at local thermodynamic equilibrium and evidence is found that the bound is satisfied if and only if a certain local thermodynamic property holds, emerging when the attempt is made to apply the bound to thin layers of matter. This property consists in the existence of an ultimate lower limit l* to the thickness of the slices for which a statistical-mechanical description is viable, depending l* on the thermodynamical variables which define the state of the system locally. This limiting scale, found to be in general much larger than the Planck scale (so that no Planck scale physics must be necessarily invoked to justify it), appears not related to gravity and this suggests that the generalized entropy bound is likely to be rooted on conventional flat-spacetime statistical mechanics, with the maximum admitted entropy being however actually determined also by gravity. Some examples of ideal fluids are considered in order to identify the mechanisms which can set a lower limit to the statistical-mechanical description and these systems are found to respect the lower limiting scale l*. The photon gas, in particular, appears to seemingly saturate this limiting scale and the consequence is drawn that for systems consisting of a single slice of a photon gas with thickness l*, the generalized Bousso bound is saturated. It is argued that this seems to open the way to a peculiar understanding of black hole entropy: if an entropy can meaningfully (i.e. with a second law) be assigned to a black hole, the value A/4 for it (where A is the area of the black hole) is required simply by (conventional) statistical mechanics coupled to general relativity. |
2205.01519 | Anna Ijjas | Timo Kist and Anna Ijjas | The robustness of slow contraction and the shape of the scalar field
potential | 23 pages, 7 figures | JCAP 8 (2022) 046 | 10.1088/1475-7516/2022/08/046 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use numerical relativity simulations to explore the conditions for a
canonical scalar field $\phi$ minimally coupled to Einstein gravity to generate
an extended phase of slow contraction that robustly smooths the universe for a
wide range of initial conditions and then sets the conditions for a graceful
exit stage. We show that to achieve robustness it suffices that the potential
$V(\phi)$ is negative and $M_{\rm Pl}|V_{,\phi}/V|\gtrsim5$ during the
smoothing phase. We also show that, to exit slow contraction, the potential
must have a minimum. Beyond the minimum, we find no constraint on the uphill
slope including the possibility of ending on a positive potential plateau or a
local minimum with $V_{\rm min}>0$. Our study establishes ultralocality for a
wide range of potentials as a key both to robust smoothing and to graceful
exit.
| [
{
"created": "Tue, 3 May 2022 14:15:01 GMT",
"version": "v1"
}
] | 2022-08-29 | [
[
"Kist",
"Timo",
""
],
[
"Ijjas",
"Anna",
""
]
] | We use numerical relativity simulations to explore the conditions for a canonical scalar field $\phi$ minimally coupled to Einstein gravity to generate an extended phase of slow contraction that robustly smooths the universe for a wide range of initial conditions and then sets the conditions for a graceful exit stage. We show that to achieve robustness it suffices that the potential $V(\phi)$ is negative and $M_{\rm Pl}|V_{,\phi}/V|\gtrsim5$ during the smoothing phase. We also show that, to exit slow contraction, the potential must have a minimum. Beyond the minimum, we find no constraint on the uphill slope including the possibility of ending on a positive potential plateau or a local minimum with $V_{\rm min}>0$. Our study establishes ultralocality for a wide range of potentials as a key both to robust smoothing and to graceful exit. |
0803.3659 | Dah-Wei Chiou | Dah-Wei Chiou | Phenomenological dynamics of loop quantum cosmology in Kantowski-Sachs
spacetime | 36 pages, 4 figures, 1 table; more errors and typos corrected;
version to appear in PRD | Phys.Rev.D78:044019,2008 | 10.1103/PhysRevD.78.044019 | IGC-08/2-4 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The fundamental theory and the semiclassical description of loop quantum
cosmology (LQC) have been studied in the Friedmann-Robertson-Walker and Bianchi
I models. As an extension to include both anisotropy and intrinsic curvature,
this paper investigates the cosmological model of Kantowski-Sachs spacetime
with a free massless scalar field at the level of phenomenological dynamics
with the LQC discreteness corrections. The LQC corrections are implemented in
two different improved quantization schemes. In both schemes, the big bang and
big crunch singularities of the classical solution are resolved and replaced by
the big bounces when the area or volume scale factor approaches the critical
values in the Planck regime measured by the reference of the scalar field
momentum. Symmetries of scaling are also noted and suggest that the fundamental
spatial scale (area gap) may give rise to a temporal scale. The bouncing
scenarios are in an analogous fashion of the Bianchi I model, naturally
extending the observations obtained previously.
| [
{
"created": "Wed, 26 Mar 2008 03:01:15 GMT",
"version": "v1"
},
{
"created": "Wed, 14 May 2008 17:37:54 GMT",
"version": "v2"
},
{
"created": "Thu, 3 Jul 2008 21:09:06 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Chiou",
"Dah-Wei",
""
]
] | The fundamental theory and the semiclassical description of loop quantum cosmology (LQC) have been studied in the Friedmann-Robertson-Walker and Bianchi I models. As an extension to include both anisotropy and intrinsic curvature, this paper investigates the cosmological model of Kantowski-Sachs spacetime with a free massless scalar field at the level of phenomenological dynamics with the LQC discreteness corrections. The LQC corrections are implemented in two different improved quantization schemes. In both schemes, the big bang and big crunch singularities of the classical solution are resolved and replaced by the big bounces when the area or volume scale factor approaches the critical values in the Planck regime measured by the reference of the scalar field momentum. Symmetries of scaling are also noted and suggest that the fundamental spatial scale (area gap) may give rise to a temporal scale. The bouncing scenarios are in an analogous fashion of the Bianchi I model, naturally extending the observations obtained previously. |
1112.2085 | Yongge Ma | Yongge Ma | Extension of Loop Quantum Gravity to Metric Theories beyond General
Relativity | 10 pages; Proceedings of Loops'11, Madrid, submitted to Journal of
Physics: Conference Series | J. Phys.: Conference Series 360 (2012), 012006 | 10.1088/1742-6596/360/1/012006 | null | gr-qc astro-ph.HE hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The successful background-independent quantization of Loop Quantum Gravity
relies on the key observation that classical General Relativity can be cast
into the connection-dynamical formalism with the structure group of SU(2). Due
to this particular formalism, Loop Quantum Gravity was generally considered as
a quantization scheme that applies only to General Relativity. However, we will
show that the nonperturbative quantization procedure of Loop Quantum Gravity
can be extended to a rather general class of metric theories of gravity, which
have received increased attention recently due to motivations coming form
cosmology and astrophysics. In particular, we will first introduce how to
reformulate the 4-dimensional metric $f(R)$ theories of gravity, as well as
Brans-Dicke theory, into connection-dynamical formalism with real SU(2)
connections as configuration variables. Through these formalisms, we then
outline the nonpertubative canonical quantization of the $f(R)$ theories and
Brans-Dicke theory by extending the loop quantization scheme of General
Relativity.
| [
{
"created": "Fri, 9 Dec 2011 12:37:48 GMT",
"version": "v1"
}
] | 2015-06-03 | [
[
"Ma",
"Yongge",
""
]
] | The successful background-independent quantization of Loop Quantum Gravity relies on the key observation that classical General Relativity can be cast into the connection-dynamical formalism with the structure group of SU(2). Due to this particular formalism, Loop Quantum Gravity was generally considered as a quantization scheme that applies only to General Relativity. However, we will show that the nonperturbative quantization procedure of Loop Quantum Gravity can be extended to a rather general class of metric theories of gravity, which have received increased attention recently due to motivations coming form cosmology and astrophysics. In particular, we will first introduce how to reformulate the 4-dimensional metric $f(R)$ theories of gravity, as well as Brans-Dicke theory, into connection-dynamical formalism with real SU(2) connections as configuration variables. Through these formalisms, we then outline the nonpertubative canonical quantization of the $f(R)$ theories and Brans-Dicke theory by extending the loop quantization scheme of General Relativity. |
2208.13481 | Kinjalk Lochan | Kinjalk Lochan | Unequal time Commutators in Friedmann universes: Deterministic evolution
of massless fields | Typos fixed, references added; Published in Topical issue of GERG In
Memory of Professor T. Padmanabhan | General Relativity and Gravitation volume 54, Article number: 100
(2022) | 10.1007/s10714-022-02991-8 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze minimally coupled massless scalar field in a Friedmann (FRW)
universe in conformal co-ordinates to model the evolution of tensor
perturbations and study the structure of the Wightman function therein. Using a
duality map from a power law FRW universe to the de Sitter universe for such
fields we obtain unequal time commutation relations between quantum field
variables. We demonstrate that the commutation relations are invariant under
state change and/or vacuum state selection. Using such commutators it is then
possible to construct out of time ordered commutators (OTOC) in the FRW
universes. The OTOCs are supposed to suggest the onset of chaotic behavior
during the quantum evolution, we see that in case of Friedmann universes,
unlike the scalar perturbations, the causal structure arrests the growth of
quantum tensor perturbations for all the relevant epochs of the universe e.g.
the de Sitter phase, the radiation dominated and the matter dominated era.
Therefore the semi classical results of having a large backreaction and
omnipresent noise in certain branches of the Friedmann universes with massless
fields such as the tensor perturbations remain robust and stable.
| [
{
"created": "Mon, 29 Aug 2022 10:29:07 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Sep 2022 14:55:49 GMT",
"version": "v2"
}
] | 2022-09-13 | [
[
"Lochan",
"Kinjalk",
""
]
] | We analyze minimally coupled massless scalar field in a Friedmann (FRW) universe in conformal co-ordinates to model the evolution of tensor perturbations and study the structure of the Wightman function therein. Using a duality map from a power law FRW universe to the de Sitter universe for such fields we obtain unequal time commutation relations between quantum field variables. We demonstrate that the commutation relations are invariant under state change and/or vacuum state selection. Using such commutators it is then possible to construct out of time ordered commutators (OTOC) in the FRW universes. The OTOCs are supposed to suggest the onset of chaotic behavior during the quantum evolution, we see that in case of Friedmann universes, unlike the scalar perturbations, the causal structure arrests the growth of quantum tensor perturbations for all the relevant epochs of the universe e.g. the de Sitter phase, the radiation dominated and the matter dominated era. Therefore the semi classical results of having a large backreaction and omnipresent noise in certain branches of the Friedmann universes with massless fields such as the tensor perturbations remain robust and stable. |
2404.19493 | Xiao Zhang | Chuxiao Liu, Xiao Zhang | Spherically symmetric Einstein-scalar-field equations for slowly
particle-like decaying null infinity | 17 pages | null | null | null | gr-qc math.DG | http://creativecommons.org/publicdomain/zero/1.0/ | We show that the spherically symmetric Einstein-scalar-field equations for
small slowly particle-like decaying initial data at null infinity have unique
global solutions.
| [
{
"created": "Tue, 30 Apr 2024 12:24:07 GMT",
"version": "v1"
}
] | 2024-05-01 | [
[
"Liu",
"Chuxiao",
""
],
[
"Zhang",
"Xiao",
""
]
] | We show that the spherically symmetric Einstein-scalar-field equations for small slowly particle-like decaying initial data at null infinity have unique global solutions. |
gr-qc/0204033 | Jun'ichi Yokoyama | Jun'ichi Yokoyama | On the origin of the cosmological constant | 5 pages. To be published in the Proc. 11th JGRG ed. by K. Maeda et al | null | null | null | gr-qc | null | Under the assumption that the cosmological constant vanishes in the true
ground state with lowest possible energy density, we argue that the observed
small but finite vacuum-like energy density can be explained if we consider a
theory with two or more degenerate perturbative vacua, which are unstable due
to quantum tunneling, and if we still live in one of such states. An example is
given making use of the topological vacua in non-Abelian gauge theories.
| [
{
"created": "Mon, 8 Apr 2002 02:16:22 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Yokoyama",
"Jun'ichi",
""
]
] | Under the assumption that the cosmological constant vanishes in the true ground state with lowest possible energy density, we argue that the observed small but finite vacuum-like energy density can be explained if we consider a theory with two or more degenerate perturbative vacua, which are unstable due to quantum tunneling, and if we still live in one of such states. An example is given making use of the topological vacua in non-Abelian gauge theories. |
gr-qc/9703072 | Frank Estabrook | Frank B. Estabrook, R. Steve Robinson and Hugo D. Wahlquist (JPL,
Pasadena) | Hyperbolic Equations for Vacuum Gravity Using Special Orthonormal Frames | 14 pages, 3 figures, LaTeX, 13 macros. CQG 14 (1997) 1237-1247 has
algebraic errors. +/- signs in Equations (2), (4) and (5) are here corrected,
and factors of 2 added to Eqs. (18) and (19) | Class.Quant.Grav. 14 (1997) 1237-1247 | 10.1088/0264-9381/14/5/025 | null | gr-qc | null | By adopting Nester's higher dimensional special orthonormal frames (HSOF) the
tetrad equations for vacuum gravity are put into first order symmetric
hyperbolic (FOSH) form with constant coefficients, independent of any time
slicing or coordinate specialization.
| [
{
"created": "Tue, 25 Mar 1997 19:28:51 GMT",
"version": "v1"
},
{
"created": "Tue, 10 Feb 2004 19:17:50 GMT",
"version": "v2"
},
{
"created": "Wed, 29 Sep 2004 23:39:23 GMT",
"version": "v3"
}
] | 2009-10-30 | [
[
"Estabrook",
"Frank B.",
"",
"JPL,\n Pasadena"
],
[
"Robinson",
"R. Steve",
"",
"JPL,\n Pasadena"
],
[
"Wahlquist",
"Hugo D.",
"",
"JPL,\n Pasadena"
]
] | By adopting Nester's higher dimensional special orthonormal frames (HSOF) the tetrad equations for vacuum gravity are put into first order symmetric hyperbolic (FOSH) form with constant coefficients, independent of any time slicing or coordinate specialization. |
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